THE    FUNDAMENTAL    PROCESSES    OF 
DYE  CHEMISTRY 


FIG.  i. — Laboratory  autoclave  fitted  with  stirring  gear.  (Constructed  of  cast-steel. 
Working  pressure  60  atms.  Capacity,  i  litre.  Weight,  33  kg.  Weight  of 
oil-bath,  ii  kg.) 

[Frontispiece. 


THE   FUNDAMENTAL  PROCESSES  OF 

DYE  CHEMISTRY 


BY 

DR.    HANS    EDUARD    FIERZ-DAVID 

PROFESSOR    OF    CHEMISTRY    AT   THE    FEDERAL     TECHNICAL 
HIGH    SCHOOL,    ZURICH 


TRANSLATED  BY 
FREDERICK  A.  MASON,  M.A.  (OxoN.),  PH.D.  (MUNICH) 

RESEARCH    CHEMIST    WITH    THE    BRITISH    DYESTTFFS    CORPORATION, 

LIMITED. 


WITH  45  ILLUSTRATIONS,  INCLUDING  19  PLATES 


NEW  YORK 

D.   VAN   NOSTRAND   COMPANY 

25,  PARK  PLACE 
1921 


rH 


Printed  in  Qreat  Britain. 


PREFACE   TO    THE    ENGLISH    EDITION 

IN  preparing  an  English  edition  of  Prof.  Fierz-David's  well-known 
work  on  the  practical  side  of  dye  chemistry,  advantage  has  been 
taken  of  the  opportunity  to  correct  one  or  two  slight  errors  that 
had  crept  into  the  original  Swiss  edition,  and  to  make  an  altera- 
tion to  Plate  XV.  For  the  rest,  the  book  remains  practically 
unaltered. 

In  most  cases  the  original  weights  and  prices  have  been  retained 
(in  francs  per  kilo.),  instead  of  trying  to  convert  them  into  shillings 
per  pound.  It  was  felt  that,  as  the  figures  referred  usually  to  pre- 
war conditions  in  Switzerland,  and  having  regard  to  the  present 
unsettled  state  of  the  exchanges  and  of  production  costs,  no  good 
purpose  would  be  served  by  attempting  to  give  the  English 
equivalents  which,  in  any  case,  would  in  all  probability  only  be 
misleading. 

I  wish  to  acknowledge,  with  much  gratitude,  the  assistance 
rendered  by  my  wife  during  the  translation  ;  and  to  Mr.  C.  Hollins 
my  best  thanks  are  due  for  his  kindness  in  giving  much  valuable 
help  in  revising  the  manuscript  and  the  proofs. 

F.  A.  MASON. 


502940 


TABLE   OF    CONTENTS 


PAGE 

Introduction  I 


I.— INTERMEDIATE   PRODUCTS 

General  Considerations      .         .         .         .         .         .         .         .         .  3 

i.— SULPHONATIONS    .         .         .         .  4-52 

/J-Naphthalene-monosulphonic  acid  and  /?-Naphthol     ....  4 
Naphthylaminetrisulphonic  acid  1:8 13 :6and  Amino-naphtholdisulphonic 

acid  (H-acid) 10 

Naphthylamine  sulphonic  acids  1 :6  and  1:7  (Cleve)     .         .         .         •  23 

Naphthylamine  sulphonic  acids  1:5  and  1 :8          .         .         .         .         •  27 

Naphtha -sultone,   Phenyl-naphthylamine    sulphonic    acid    1:8,  Amino- 
naphthol  sulphonic  acid  1 18:4  and  Amino-naphtholdisulphonic  acid 
1:8:2:4  (S-acid  and  SS-acid)          .         .         .         .          .         .         -3° 

Amino-naphthol  sulphonic  acid  1:5:7           .          .          .          .          •  31 

Naphthol  sulphonic  acid  2:6  (Schaffer  acid)  .          .          .          .          -33 

Naphthol  disulphonic  acids  2:3:6  (R-acid)  and  2:6:8  (G-acid)       .          .  34 

Amino-naphthol  sulphonic  acids  2:6:8  and  2:5:7  (Gamma  and  J-acids)  .  35 

Naphthylamine  disulphonic  acids  2:5:7,  2.:6:8,  2:1:5,  Gamma  acid         .  40 

Amino-naphthol  sulphonic  acid  2:5:7  (J-acid)      .....  41 

Nitrobenzene-sulphonic  acid  and  Metanilic  acid            .          .          .          •  41 
Sulphanilic  acid          .          .          .          .          .          .          .          .          .          -43 

Naphthionic  acid  (Naphthylamine  sulphonic  acid  1:4)           ...  45 
Meta-nitraniline  sulphonic  acid  1:3:4           .          .          •          •          •          .46 
1 :2:4-Phenylenediamine  sulphonic  acid  from  Dinitro-chlorbenzene          .  46 
Para-Nitraniline  sulphonic  acid  from  Para-nitro-chlorbenzene         .         .  48 
Diaminodiphenylamine  sulphonic   acid  and    Aminodiphenylamine   sul- 
phonic acid         ..........  49 

i:2:4-Amino-naphthol   sulphonic    acid    from    ^-Naphthol,   "  Dioxine," 
Eriochrome  Blue  Black  B,  Eriochrome  Black  T  and  A,  Para-Amino- 

phenol  disulphonic  acid  from  Nitroso  dimethyl  aniline   .                   .  50 


viii  TABLE   OF    CONTENTS 


2.— NITRATIONS   AND   REDUCTIONS      .         53-82 

Nitrobenzene  from  Benzene .          .         .       53 

Meta-Dinitro-benzene  from  Nitrobenzene 54 

Aniline  from  Nitrobenzene         .         .         .         .         .          .          .         .        55 

Benzidine  from  Nitrobenzene     .         .         .         .    .  .         .  56 

Hydrazobenzene        .         .         .         .         .         .         .         .         .  58 

2 :2f-Benzidine  disulphonic  acid  from  Nitrobenzene       ....        62 

Phenylhydrazine  sulphonic  acid  from  Sulphanilic  acid  .  .  .  »  64 
Meta-Nitraniline  from  Meta-Dinitrobenzene  .  .  .  .66 

Nitro-amino-phenol .          .          .66 

Meta-Phenylene-diamine  from  Meta-Dinitro-benzene  ....  67 
Para-Nitraniline  and  Para-Amino-acetanilide  from  Aniline  ...  69 
Ortho- and  Para-Nitrophenol  and  their  Alkyl  ethers  .  .  .  -73 
Method  of  introducing  alkyl  chlorides  into  a  laboratory  autoclave  .  74 

Trinitrophenol  (picric  acid),  Naphthol  Yellow  S,  Martius  Yellow          .       76 

Picramic  acid  from  Picric  acid 77 

Metachrome  Brown  ..........        79 

a-Nitronaphthalene  and  a-Naphthylamine  from  Naphthalene  .  .  79 
1 :2.'4-Aminonaphthol  sulphonic  acid  from  Nitronaphthalene  .  .  82 

3.— CHLORINATIONS    .         .        .         83-92 

Chlorbenzene  from  Benzene       .         .         .         .  .         .         .         -83 

Dinitrochlorbenzene  from  Chlorbenzene      .          .  .        ..         .    -      .        86 

Some  condensation  products  of  Dinitrochlorbenzene  ....        87 

Benzal  chloride  and  Benzaldehyde  from  Toluene  .          .          .          .88 

2:6-Dichlorbenzaldehyde  from  Ortho-nitrotoluene  ....        89 

2:6-Chlortoluidine    .         .         .  :      .         .         .  .         .         .         .       90 

2:6-Dichlortoluene     .         .         ....  .         .         .         .       91 

2:6-Dichlorbenzalchloride .         .'      ..         .       ',  .    :      .          .          .       92 

4.— OXIDATIONS         .        .        .        93-97 

Dinitro-stilbene-disulphonic  acid  from  Para-nitrotoluene        .          .          -93 
Diamino-stilbene-disulphonic  acid        .......       94 

Anthraquinone  from  Amthracene         .          .          .          .          .          .          -95 

5.— CONDENSATIONS    .        .        .       97-107 

Diphenylamine  from  Aniline  and  Aniline  salt       .         .          .,       •     ,    •  97 

)8-Naphthylamine  from  /3-Naphthol     .         ../,..         .         •  9^ 

Phenyl-y-acid   ....         »         •  ,                                                     .  101 

Nevile  &  Winther's  acid  (Naphthol  sulphonic  acid  1:4)      ..,....'.  101 


TABLE   OF   CONTENTS  ix 


PAGE 


a-Naphthol  from  a-Naphthylamine     .  .      102 

Dimethylaniline  (Diethylaniline,  Ethylbenzylaniline)   .  .102 

Salicylic  acid  from  Phenol                     .  .     105 

Ortho-Cresotinic  acid          .          .          .          .  .106 

Gallamide  and  Gallic  acid  from  Tannin      .          .      v  *  .'.        ...         .     106 


II.— DYES 

6.— AZO   DYES  ..        .        .      108-145 

Diazotization  of  Amines,  Aniline,  etc.,  /-Nitraniline,  etc.,  a-Naphthyl- 
amine, Sulphonic  acids,  Benzidine,  etc.      ...»          .          .      108-110 

Coupling  of  an  Azo  Component        "  .          .          .•         .          .          .        . .  J 1 1 

Acid  Orange  A  or  Orange  II                .         .         .         .         .         .         .  113 

Acetyl  H-acid  and  Aminonaphthol  Red  G            .         .         .         .         .  114 

Acid  Anthracene  Red  G  and  Chromocitronine     ,         .         .         .  1 1 5 

Bismarck  Brown  G  and  R            .          .          .         *         .          ..          .  116 

Benzidine  colours       .         .       '  ;    •     .•         ,         .         .         ...        .  118 

The  intermediate  compound  from  Benzidine — Salicyclic  acid        .         .  118 

Diamine  Brown  V  and  Diamine  Fast  Red  F        .         .         .                   .  119 

Dianil  Brown  3GN,  Sulphochrysoidine    "   .         .         ».       .         .         .  120 

Diamine  Green  B  (Cassella)        .         .         .         .",-..       .         .        '.         .  122 

Naphthol  Blue  Black  B  and  Azo  Dark  Green       .         ''M     .         .         .  122 

Direct  Deep  Black  EW  (Bayer)           .         ..        .         .-      .         .         .  125 

Congo  Red        ......       ...          .      ;   . .  r      .          .  127 

Tropaeoline  or  Orange  IV  from  Diphenylamine  and  Sulphanilic  acid     .  1 29 

Azo  Yellow  R  &  G  (Weiler-ter-Meer)         .         ."       .      :.         .     u\  131 

Aminoazobenzene  from  Aniline  ;  Fast  Yellow     .          .          .          ."        ..  133 

Azo  Flavine  FF  (BASF)    .         .          .         .      -*         .                   .       :.  136 

Fast    Light   Yellow   C   (Bayer)  from  Phenylhydrazine  sulphonic  acid, 

Acetoacetic  Ester  and  Aniline 137 

Eriochrome  Red  B  and  Polar  Yellow  5 G     .         ,..         .         .          .      I37~I39 

Chrysophenine  GOO  from  Diaminostilbene  disulphonic  acid           .          .  139 

Ethylation  of  Brilliant  Yellow    .         .         .         ...         .         .  140 

Benzo  Fast  Blue  FR  (Bayer)  from  Aniline,  Cleve  acid  1:7,  and  J-acid   .  141 


7.— TRIPHENYLMETHANE   DYES          .      145-152 

Malachite  Green        -.         .          .    -      .V      ^_       ^         .     :    ..        .        >      145 
Xylene  Blue  VS  (Sandoz)  .          .         .          .  ...;.,>.      148 

Benzaldehyde  disulphonic  acid  1:2:4  .        V.     .         .     .  :,-,..    ".       -;.     150 


TABLE   OF   CONTENTS 


PAGE 


8.— SULPHUR   MELTS   .                 .  152-161 

Primuline  (Green)     .         . 152 

Separation  of  crude  Primuline  melt      .          .          .          .          .          .  153 

Naphthamine  Yellow  NN  (Kalle)        ...         .         .         .         .  .      155 

Thiazole  Yellow        .         .         .         .         .         .         .         .          .  .156 

Sulphur  Black  T  (AGFA)  from  Dinitrochlorbenzene  .         .         .  .     157 

Auramine  00  (Sandmeyer)           .         .          .         .         .         .         .  159 

Tetramethyldiaminodiphenylmethane 159 

9.— MISCELLANEOUS   DYES       .        .  161-185 

Sandmeyer's  'Indigo  synthesis       .         .         .          .         .         .         .  .161 

"  Thiocarbanilide " 163 

"  Hydrocyancarbodiphenylimide "        .          .          .          .          .  .163 

"  Thioamide "  (Thiooxamine-diphenylamidine)     .          .          .  .164 

a-Isatin-anilide,  Ciba  Scarlet  and  Violet        .          .          .          .  .164 

a-Thioisatin        .         .          .          .          .          .          .          .          .  .165 

Alizarin  from  pure  Anthraquinone  :    .          .          .          .          .          .  .167 

Silver  Salt           •.        •         •   ' .167 

Alizarin  melt .         .  .168 

Anthracene  Brown  FF  (Anthragallol)           .         .          .         .         .  .170 

Gallamine  Blue  from  Gallamide           .         .         .         .         .         .  -171 

^-Nitroso-dimethylaniline,  and^-Nitroso-diethylaniline          .  .      171 

Gallamine  Blue  paste           .         .         .         .         .         .         .  .172 

Modern  Violet           .         .         .         .         .         .         .         .         .  -173 

Celestine  Blue  and  Gallocyanine          .         .         .         .         .         .  .173 

Meldola's  Blue,  Naphthol  Blue,  or  Bengal  Blue  .         .         .         .  173 

Methylene  Blue  from  Dimethylaniline          .          .          .          .          .  175 

/-Aminodimethylaniline       .       "  .          .   *      .          ."_'..  .     175 

Thiosulphonic  acid  of  Bindschedler's  Green           .         .        V  .      175 

Methylene  Blue,  zinc-free  .         .         .         .         .        ".'"'.  .     177 

Methylene  Green 177 

Thiazine  Blue  or  Thionine  Blue         .          .         .         .          .         .  .178 

Lauth's  Violet  .         .         .         .         .         .         .         .         .         .  .178 

Safranine  from  0-Toluidine  and  Aniline        .          .          .          .         .  .178 

Regeneration  of  bichromate         .          .          .          .          .          .          .  .181 

Clematine          .         .         .         .         .         .         .         .         .         .  .182 

Indoine,  Janus  Black           .          .          .          ...          .          .  .      182 

General  remarks  upon  the  utilization  of  by-products  and  the   relative 

values  of  various  methods  of  manufacture       .         .         .         .      ••  .     182 

o-  and  /J-Nitrochlorbenzene      .         .         .         .         •         •  •     183 

R-andG-salt                   .         ....     ...      •       ..     !,  .  .'    183 


TABLE    OF    CONTENTS  xi 


PAGE 


Various  methods  of  preparation  of  S-acid,  c-acid    j    ...  .               1 84 

Anthranilic  acid,  Chlorbenzoic  acid,  Azo-salicylic  acid  .          .185 

Eriochrome  Flavine  A     ....          .         ....         .    .  .;i  *     *^5 

io.— SUMMARY   pF   THE    MOST   IMPORTANT 

METHODS     .         .         .  ;      186-187 

Sulphonations    .          .          .          .          .          ...  .          .      186 

Nitrations          ....  .186 

Reductions         ....                   ...  .186 

Oxidations          .  .186 

Alkali  fusions     .         .  .187 

Methods  of  coupling           .          .         ...         .  .187 


III.— TECHNICAL   DETAILS 

ii.— VACUUM  DISTILLATIONS  IN  THE   LABORATORY 

AND   ON   THE   WORKS        '.         .        .     188 

Diphlegmation,  Kubierschky  column,  Raschig  column           .       .  ...  .      188 

Vacuum  pumps           .        -.         .         .         .        ..        ...  .       .         .  .189 

Apparatus  for  the  distillation  of  Naphthols  .         .         .         ....  ,.189 

Apparatus  for  distillation  under  reduced  pressure  in  the  laboratory  ..     192 

I2._NOTES   UPON   THE   CONSTRUCTION   AND   USE 

OF   AUTOCLAVES    .        .         .         193-203 

Description    of    autoclaves    and     structural    material    (material,    liner, 
stuffing-box,  safety-valve,  thermometer,  stirrer,  etc.),  setting  up  and 

working,  methods  of  heating        .......  193 

Laboratory  autoclave  .         .  198 

Rotary  autoclaves       .  .  „  -.;,  *         .         .         .          .         .          .  200 

General  rules  for  the  use  of  pressure  vessels  .         .         .          .         .  200 

Pressure  curve  for  aqueous  caustic  soda  of  various  concentrations .  .         .  202 


13.— STRUCTURAL    MATERIALS   USED   IN   DYE 

CHEMISTRY    .         .         .        .      203-210 

Metals       .  ..........     203 

Non-metals        .         .         .         .         .  -.    .  *  .         .         .         .     206 

Structural  materials  of  organic  origin  .        -.         .         .         .    -     .         .     208 


xii  TABLE    OF    CONTENTS 

14.— TECHNICAL    NOTES    ON  .WORKS    MANAGE-       PAGE 
MENT          .         .         .         .         .      210 

Significance  of  the  dye  industry  ;  specialities  and  mass  production  ; 
"  Interessengemeinschaften  "  or  "  Rings "  ;  arrangement  of  a 
modern  colour  factory  ;  organization  ;  ivories  ;  expenses  ;  steam 
consumption  ;  utilization  of  steam,  compressed  air  and  vacuum  ; 
duties  of  the  works  chemist  ;  manufacture  ;  standard  colours  ; 
drying  ;  making  up  to  type  ;  grinding  ;  mixing  .  .  210-218 

,       15.— EXAMPLE   OF  COSTING  OF  A  SIMPLE  DYE  218 

Orange  II.  ;  melt  of  sodium  salt  of  /3-naphthalene-monosulphonic  acid  ; 

sulphanilic  acid  ;  /?-naphthol       .          .          .          .         ,         .       218-223 


IV.— ANALYTICAL   SECTION 

1 6.— ANALYTICAL   DETAILS      .    '     .         ,     224 

General  ;  preparation  of  standards  for  titration  ;  estimation  of  amines, 
naphthols,  dihydroxynaphthalene,  aminonaphthol  sulphonic  acids, 
naphthol  sulphonic  acids,  dihydroxynaphthalene  mono-  and  di- 
sulphonic  acids ;  the  common  test  papers  ;  reagent  solutions  for 
"spotting"  on  filter-paper;  estimation  of  zinc  dust  and  lead 
peroxide  paste  .  .  .  .  •  224-235 

INDEX  '•     236 


LIST   OF    FIGURES   AND   PLATES 

FIG.                 PLATE  PAGE 

1.  I.  Laboratory  autoclave  with  stirrer         ...       .     Frontispiece 

2.  Sulphonating  pot  for  naphthalene  sulphonic  acid     .          .          5 

3.  Fusion  pot  for  /?-naphthol     .          »  .          .          .          8 

4.  Autogeneously  welded   sulphonating  pot   for  use    with 

oleum,  etc.       .         .         .         .         .          .          .         .11 

5.  Apparatus    with    propeller    stirrer    for    reductions    by 

Bechamp-Brimmeyr  method  .          .          .  17 

6.  II.  Sulphonating  and  nitrating  pot  in  wooden  tub        .          .     (12) 

7.  II.  Steam-jacketed  sulphonating  and  nitrating  pot         .          .     (12) 

8.  III.     Hydraulic  press    .  (24) 

9.  Heating  under  reflux  condenser  with  stirring          .          .        47 

10.  IV.  Nitrating  pot  with  helical  stirrer  .....    (38) 

11.  IV.  Reduction  pot  with  propeller  stirrer       .         .'       .         .    (38) 

12.  V.  Separating  funnel  and  extracting  vessel                      ;        ..    (52) 

13.  V.  Centrifuge  with  underneath  drive           .          ,'f     ".          .    (52) 

14.  VI.  Stone  vacuum  filter  for  strongly  acid  precipitates     .         .    (62) 

15.  VI.  Frame  filter  for  crystalline  precipitates  ....    (62) 

1 6.  Small  gas  cylinder  for  adding  alkyl  chloride   ...        74 
i6A.  Method  of  filling  a  laboratory  autoclave  with  alkyl  chloride        75 

17.  Apparatus  for  distilling  in  superheated  steam  .         .       81 

1 8.  Witt's  Bell-stirrer 84 

i8A.  Heating  under  a  reflex  condenser  and  stirring  with  an 

ordinary  bulb  condenser         .         .         .         .          .84 

19.  Large-scale    apparatus    for   distilling    with    superheated 

steam  ...         .         .         .         ,         .         .99 

20.  VII.  Arrangement  of  a  colour  shed        .         .         .         .        (76-77) 

21.  Calibrated  vessel  for  coupling         .          .          .          .          .112 

22.  Laboratory  vacuum  filter  or  "  nutsch "  .          .          .     .114 

*"  I    VIII.  Autoclaves  for  steam  or  hot-water  heating  (Frederking)     .  (90) 
24.3 

>      IX.  Kubierschky  columns    .        '.          .         ..         -.          ..        •  (102) 
2  5  A.  J 


XIV 


LIST   OF    FIGURES    AND   PLATES 


26. 

27. 

28. 
29. 
30- 


IX. 

X. 

XI. 
XI. 
XII. 
XII. 
XIII. 


32- 
33- 
34- 
35- 
36. 
37- 
38. 
38A. 

39- 
40. 

41. 
42. 

4-3- 

44.  XVIII. 

45.  XIX. 


XIV. 

XIV. 

XV. 


XVI. 

XVI. 

XVII. 


Raschig  column    .         .         ... 
Laboratory  vacuum  distillation 
Works  plant  for  vacuum  distillation 
Oil-jacketed  autoclave  for  stiff  melts 
Section  of  autoclave     .         .         . 
Large  cast-iron  autoclave  with  steam  heating 
Large  cast-steel  autoclave       .         . 
Stirring  autoclave  of  Plate  I.  taken  apart 
Section  through  a  laboratory  autoclave  . 
Small  cast-steel  autoclave       .         ...         . 
Small  cast-iron  autoclave  with  stirrer 
Wrought-iron  rotating  autoclave    . 
Section  through  rotating  autoclave 
Details  of  rotating  autoclave 
Diagram  of  a  "  Perplex  "  disintegrator   . 
Passburg  drying  chest  .          .          .         .    '      . 
Rotary  compressor  and  vacuum  pump    . 
Disintegrator  for  colours       . 
Distillation  of  high- boiling  liquid 
Colour  mixing  machine  (Hoechst  system) 
Screw-press  ..... 


PAGE 
(102) 

191 
(112) 
(126) 
(126) 


(138) 


199 
(l64) 
(164) 


201 
201 

217 

(188) 
(188) 
(208) 

227 


(224) 


INTRODUCTION 

ALTHOUGH  well  aware  of  the  existence  of  a  large  literature  dealing 
with  laboratory  practice,  I  have  written  this  book  because  there  does 
not  appear  to  exist  a  suitable  introduction  to  the  fundamental 
operations  of  dye  chemistry. 

Ignorance  of  elementary  facts  leads  in  practice  to  waste  of  time, 
which  may  be  redeemed  in  part  by  suitable  instruction  ;  nor  should 
it  be  forgotten  that  many  of  the  essential  features  of  chemical  craft 
may  be  learnt  from  books. 

The  manufacture  of  synthetic  colours  has  attained  to  such 
importance  that  it  seems  desirable  to  familiarize  the  rising  generation 
of  chemical  technologists  with  the  methods  of  production  of  the  more 
important  intermediates.  With  this  end  in  view,  I  have  attempted 
a  description  of  these  methods  in  a  manner  which  may  be  helpful 
even  to  those  unfamiliar  with  technical  operations. 

Azo  colours  form  the  largest  section  of  artificial  dyes,  and  in 
consequence  most  attention  has  been  devoted  to  the  ^preparation  of 
the  necessary  intermediates.  As,  however,  many  of  these  inter- 
mediates are  also  used  in  the  synthesis  of  other  classes  of  dyes,  such 
as  Indigo,  Azines,  Thiazines,  Aniline  Black,  Sulphur  colours,  and 
Triphenyl-methane  dyes,  it  may  fairly  be  claimed  that  the  field  of 
synthetic  colours  in  its  essential  features  is  covered  by  the  present 
volume. 

To  complete  the  picture  I  have  added  recipes  for  a  few  dyes 
and  included  some  general  observations  on  the  technique  of  dye 
manufacture.  With  only  trifling  exceptions  the  dyes  dealt  with 
can  all  be  obtained  from  the  intermediates  described  in  the  first 
portion,  so  that  the  student  is  enabled  to  obtain  a  clear  view  of 
the  stages  of  development  of  a  dye. 

In  this  industry  there  are  certain  fundamental  operations  which 
are  constantly  repeated  with  slight  but  important  modifications  ; 
for  this  reason  I  have  purposely  given  the  first  few  recipes  in  as 
great  detail  as  possible,  and  frequent  references  will  be  made  to 
them  later. 

I  have  also  attempted  to  describe  the  processes  in  such  a  way  as 
to  give,  besides  the  laboratory  details,  a  clear  indication  of  the  method 

i  J 


2  INTRODUCTION 

of  carrying  out  the  process  in  the  works.  There  would  be  no  point 
whatever  in  giving  either  laboratory  recipes  or  works  recipes  alone, 
as  only  by  an  acquaintanceship  with  both  can  the  budding  chemist 
get  an  insight  into  the  technical  side  of  the  dye  industry,  since 
laboratory  and  works  must  be  regarded  as  parts  of  an  indivisible 
whole. 

I  wish  also  to  emphasize  the  fact  that  any  process  which  is 
successful  in  the  laboratory  will  also  succeed  on  the  large  scale 
when  the  necessary  alterations  for  dealing  with  the  larger  quantities 
involved  have  been  made  ;  this  may,  indeed,  be  regarded  as  a 
fundamental  principle  by  every  technical  chemist. 

Lastly,  I  would  observe  that  the  use  of  too  little  material  in 
technical  laboratory  experiments  leads  to  inaccurate  results.  For 
this  reason,  it  is  the  general  practice  to  measure  the  laboratory 
charge  in  gram-molecules  which,  multiplied  by  a  thousand,  gives 
at  once  the  scale  for  works  practice. 

Too  much  stress  cannot  be  laid  on  the  fact  that  the  material 
of  which  the  apparatus  is  constructed  plays  an  important  part  in 
every  process  ;  for  this  reason  every  chemist  should  be  quite  clear 
in  his  own  mind  as  to  the  suitability  of  various  materials  for  different 
chemical  processes,  as  by  this  means  he  will  be  able  to  avoid  many 
an  unwelcome  breakdown. 

Objection  may  be  taken  to  the  fact  that  the  patent  literature 
of  the  subject  has  been  almost  entirely  neglected  ;  this,  however, 
has  been  done  on  purpose,  as  the  beginner  is  as  likely  as  not  to  be 
confused  by  numerous  references.  Those  who  desire  information 
on  patents  will  find  all  they  require  in  the  excellent  collections  of 
patents  compiled  by  Friedlaender  and  by  Winther.  In  these  volumes 
a  short  summary  is  given  for  each  class  of  dyes,  including  references 
to  all  the  important  work  on  the  subject.  In  my  opinion,  it  is  far 
better  for  the  beginner  to  get  a  good  knowledge  of  the  few  facts 
that  he  will  find  in  any  reliable  text-book  of  organic  chemistry  than 
to  attempt  to  become  acquainted  with  the  confusing  details  of 
innumerable  patents. 

The  recipes  given  in  this  book  must,  of  course,  only  be  regarded 
in  the  light  of  finger-posts,  and  they  make  no  claim  to  be  the  best, 
for  many  paths  lead  to  Rome.  All  the  examples  given,  however, 
have  been  actually  tested  by  the  author,  and  in  the  majority  of  cases 
they  have  also  been  put  through  in  the  works,  under  his  supervision, 
so  that  they  may  be  regarded  as  being  technically  satisfactory.  . 

H.  E.  F, 


THE    FUNDAMENTAL   PROCESSES  OF 

DYE  CHEMISTRY 

I.    INTERMEDIATE    PRODUCTS 

General  Considerations. 

THE  term  Intermediate  Products  is  applied,  in  the  dye  industry, 
to  those  substances  obtained  from  organic  products,  whether 
aromatic  or  aliphatic,  which  are  devoid  of  dye  character.  The  most 
important  raw  materials  are  Benzene  and  its  homologues,  Naphtha- 
lene and  Anthracene,  and,  to  a  lesser  extent,  certain  aliphatic  bodies 
such  as  Methyl  and  Ethyl  alcohol,  Acetic  acid,  and  various  other 
less  important  substances  which  are  utilized  chiefly  for  special 
brands  of  colours. 

From  these  raw  materials  the  intermediate  products  are  obtained 
by  means  of  certain  comparatively  simple  chemical  operations  ; 
the  hydrocarbons  which  serve  as  the  starting-point  are  obtained  by 
the  colour  factories  from  the  tar  distilleries.  In  many  cases  it  is 
found  that  the  yields  obtained  can  be  increased  almost  up  to  the 
theoretical  by  paying  scrupulous  attention  to  all  the  conditions. 
For  this  reason,  as  was  indicated  in  the  Introduction,  the  recipes 
have  -been  given  in  almost  exaggerated  detail,  but  every  technical 
chemist  will  agree  with  me  that  a  good  recipe  cannot  be  given  too 
accurately,  for  quite  slight  errors  may  often  cause  very  considerable 
variations  in  the  final  product. 

It  has  further  been  found  that  the  manufacture  of  the  intermediate 
products  is  far  more  difficult  than  that  of  the  finished  colouring 
matters,  and,  in  addition,  the  apparatus  and  machinery  needed  for 
the  intermediates  occupies  a  far  greater  space  than  that  required  for 
the  actual  dyes.  The  Anthraquinone  dyes,  however,  form  an 
exception  to  this  generalization.  With  the  exception  of  this  last 
case  it  may  be  said  that  the  ratio  of  the  size  of  the  installations 
and  the  number  of  workmen  required  for  intermediates  and  dyes 
respectively  is  approximately  as  3:1,  or,  in  other  words,  a  colour 
factory  which  has  previously  purchased  its  intermediates  and  now 
intends  to  make  them  itself  must  enlarge  itself  about  fourfold. 

3 


jfi  INTERMEDIATE  PRODUCTS 

Further,  it  is  found  that  the  apparatus  used  for  the  production 
of  Intermediates  is  very  rapidly  destroyed  by  the  chemicals  used, 
which  is  hardly  surprising  when  one  considers  that  for  the  most 
part  they  have  strong  acids  and  alkalis  to  deal  with.  For  these 
reasons,  in  a  well-conducted  factory,  all  the  apparatus  should  be 
fully  written  off. 

It  may  be  pointed  out  at  once  that  the  arrangement  of  the  Inter- 
mediate Products  which  has  been  selected  in  the  first  part  of  this 
book  will  hardly  bear  serious  criticism  from  the  purely  scientific 
standpoint.  I  have,  for  instance,  under  the  heading  of  Sulphona- 
tions  included  quite  a  number  of  other  operations.  This  arbitrary 
choice,  however,  will  be  found  to  justify  itself  in  the  sequel,  since  it 
is  obviously  undesirable  that  a  product  such  as  Aminonaphthol- 
disulphonic-acid  1:8:3:6  (H-acid)  should  be  dealt  with  under 
four  different,  headings  ;  any  such  attempt  would  obviously 
be  contrary  to  the  dictates  both  of  convenience  and  of  common 
sense. 

For  the  rest,  the  Index  will  afford  any  further  information  in 
cases  of  doubt. 

i.    SULPHONATIONS 

j8-Naphthalene-monosulphonic  Acid  and  j3-Naphthol. 
Reaction  : 


SO.H 


85% 


This  product  may  be  prepared  by  several  different  methods.  If 
the  j8-monosulphonic  acid  is  to  serve  for  the  preparation  of 
/J-Naphthol,  the  sulphuric  acid  must  be  completely  utilized,  as  the 
product  is  so  cheap  that  only  the  best  process  is  capable  of  com- 
peting. (For  further  details,  see  /3-Naphthol.)  The  method  for 
preparing  the  Di-  and  Tri-sulphonic  acids  is  given  under  H-acid. 

The  sulphonation  of  naphthalene  at  elevated  temperatures 
(170°  C.)  leads  to  the  formation  of  naphthalene  jS-sulphonic  acid. 
A  certain  quantity  of  the  alpha  acid  is  always  produced  at  the  same 
time,  amounting  to  about  15%  at  least,  according  to  the  results 
obtained  by  various  experimenters.  The  researches  of  O.  N.  Witt l 

1  Berichte,  1915,  p.  743. 


SULPHONATIONS  5 

have  shed  a  good  deal  of  light,  in  certain  directions,  on  the  complex 
relationships  involved.  In  actual  practice,  however,  where  it  is 
necessary  to  obtain  the  highest  possible  yield  of  /3-naphthol  from 
the  minimum  possible  quantity  of  sulphuric  acid,  Witt's  process  is 
hardly  suitable. 

The  following  quantities  give  satisfactory  results  : — 

260  gms.  Naphthalene  =  2  mols. 

280  gms.  Sulphuric  acid,  66°  Be.  =  93  %. 

The  naphthalene  used  must  be  perfectly  pure,  must  have  no  un- 
pleasant tarry  odour, 
and  should  not  dis- 
colour on  heating  in  a 
test-tube  with  concen- 
trated sulphuric  acid. 
The  German  tar- distil- 
leries used  to  deliver 
naphthalene  which  met 
every  requirement. 

Laboratory  Appara- 
tus (see  Fig.  2). — This 
consists  of  a  sheet-iron, 
or,  better,  a  cast-iron 
(or  porcelain  or  glass), 
beaker  of  about  n  cm. 
diameter  and  some  20 
cm.  high.  A  well-fitting 
cover  made  of  sheet  lead 
is  provided,  through 
which  pass  the  stirrer, 
thermometer,  and  tube 
for  the  addition  of  the 
acid.  The  type  of  stirrer 
shown  in  the  figure 
has  been  found  very 
suitable  ;  it  can  be 
readily  made  from  glass 
rod,  and  may  be  used 
for  all  purposes  where 
the  mechanical  strain  is 
not  too  great.  In  general,  however,  iron  is  to  be  preferred.  The 
sleeve  carrying  the  stirrer  is  best  made  of  copper,  as  both  glass  and 


260  gms. 
Naphth. 
280  gms. 
H2SOd. 


FIG.  2. — Sulphonating  pot  for  naphthale 
sulphonic  acids. 


6  INTERMEDIATE   PRODUCTS 

iron  run  very  freely  on  copper  on  a  small  scale,  and  it  does  not 
tend  to  "  corrode  "  the  stirrer  so  much.  The  driving  pulley  may 
be  made  of  bronze,  as  this  metal  also  runs  very  well  on  copper, 
especially  if  vaseline  be  used  as  a  lubricant.  The  thermometer 
should  have  the  scale  on  the  upper  portion,  and  should  dip  down 
as  far  as  possible.  Further,  I  may  remark  that  in  all  cases  where  it 
is  necessary  to  watch  the  addition  of  any  liquid  very  carefully,  a 
dropping  funnel  with  a  drop-counter  (as  shown)  should  be  used. 
The  pot  must  stand  on  a  good  substantial  retort-stand,  and  the 
copper  "  sleeve  "  must  -be  fixed  with  a  strong  clamp.  The  ther- 
mometer and  the  dropping  funnel  must  also  be  fixed  firmly  and  in 
such  a  manner  that  the  stirrer  cannot  come  in  contact  with  either. 

The  weighed  quantity  of  naphthalene  is  heated  directly  in  the 
beaker  to  165°,  with  continuous  stirring.  As  soon  as  this  temperature 
has  been  attained  the  sulphuric  acid  is  allowed  to  run  in  during  half 
an  hour,  the  gas  being  so  regulated  that  the  temperature  remains 
constant  between  163°  and  168°.  The  dropping  funnel  is  then 
removed,  its  place  being  taken  by  a  bent  glass  tube,  which  is  fitted 
tightly  to  the  cover  by  means  of  cork  or  asbestos  paper.  Water  and 
naphthalene  distil  off  through  this  tube  during  the  course  of  the 
sulphonation.  The  mixture  of  naphthalene  and  sulphuric  acid  is 
now  kept  at  165°  for  an  hour  with  continuous  stirring,  then  for  one 
hour  at  167°,  then  at  170°  for  an  hour,  and,  finally,  for  an  hour  at 
173°.  During  this  operation  about  30  gms.  water  and  25  gms. 
naphthalene  can  be  collected  in  the  receiver.  An  appreciable 
amount  of  naphthalene  also  condenses  by  degrees  on  the  cover  of 
the  vessel,  but  may  be  disregarded.  The  flame  is  then  removed, 
'and  the  apparatus  dismantled.  The  resultant  mixture  contains, 
besides  naphthalene  sulphonic  acid,  a  certain  quantity  of  sulphones, 
a  little  free  sulphuric  acid,  and  some  disulphonic  acids,  together 
with  some  resinous  matters.  The  product  should  be  colourless. 
1*8  1.  Water.  It  is  then  poured  into  r8  litres  water.  The  further  working  up 
may  be  carried  out  in  numerous  ways,  and  many  differ ent  methods 
are  adopted  in  the  various  factories.  Some  partially  neutralize  and 
then  salt  out  the  naphthalene  sulphonic  acids.  Others  prefer  to 
"  lime  out  "  first,  then  converting  into  the  sodium  salt  by  means  of 
Glauber  salt,  after  which  the  calcium  sulphate  is  filtered  off,  the 
residue  being  evaporated  down  and  then  worked  up  further.  The 
simplest  method  is  to  salt  out  directly  without  attempting  to  neutralize 
at  all,  but  this  has  the  disadvantage  that  the  strongly  acid  filtrate 
rapidly  destroys  both  filter-cloths  and  filter-presses,  and  also  that 
on  drying  the  sodium  salt  of  the  monosulphonic  acid  the  entire 


SULPHONATIONS  7 

vicinity  is  polluted  by  the  great  quantities  of  hydrochloric  acid  which 
are  given  off. 

The  solution  of  the  free  sulphonic  acids  is  now  partially  neu- 
tralized by  sprinkling  in  60  gms.  of  soda,  with  good  stirring.  60  gms.  soda. 
360  gms.  of  common  salt  are  then  added  slowly  ;  after  a  short  time 
the  liquid  begins  to  solidify  to  a  mass  of  large  lumps  which  make 
further  stirring  very  difficult.  Nevertheless,  the  stirring  must  be 
continued  until  the  mass  again  appears  to  be  completely  homogeneous, 
as  only  by  this  means  can  one  ensure  that  the  salt  will  be  completely 
dissolved  and  that  a  precipitate  will  be  obtained  which  will  filter 
well.  The  actual  amount  of  stirring  required  depends  upon  the 
speed  of  rotation  of  the  stirrer,  but  in  any  case  at  least  6  hours  will 
be  requisite,  otherwise  the  separation  will  be  incomplete.  The 
precipitate  is  then  introduced  into  a  suction  filter  provided  with  a 
cotton  filter  cloth  and  thoroughly  pressed  down.  After  removal 
from  the  filter  the  product  is  placed  in  a  strong,  moistened  cotton 
cloth  and  pressed,  gently  at  first,  and  then  more  energetically,  in  a 
screw  press.  The  pressing  should  take  at  least  2  hours,  otherwise 
too  much  mother-liquor  remains  in  the  cake.  The  hard  mass  .is 
then  ground  up  and  dried  completely  at  100-120°  C. 

The  yield  of  "  f$-salt  "  is  about  165  %,  calculated  on  the  weight 
of  naphthalene  taken,  which  corresponds  in  this  case  to  a  yield  of 
400—420  gms. 

The  mother-liquors  can  be  worked  up  for  Glauber's  salt ;  it 
contains  a  little  a-acid,  together  with  resins  and  traces  of  /3-acid. 

The  Melt  of  the  sodium  naphthalene  sulphonate  is  one  of  the 
most  important  operations  of  applied  organic  chemistry.  When 
one  considers  the  very  low  price  obtained  for  Naphthol  it  is  hardly 
surprising  that  only  quite  a  few  factories  manufacture  this  product. 
Cheap  raw  materials,  such  as  coal,  soda,  and  sulphuric  acid,  are,  of 
course,  essential.  The  waste  heat  from  the  melt  pots  must  be 
utilized  for  drying  the  sodium  salt  and  the  Glauber's  salt  and  sulphite 
produced  as  by-products,  or  the  sulphurous  acid  must  be  recovered. 
A  naphthol  works  that  does  not  completely  recover  all  its  by-products 
is  incapable  of  competing  in  the  open  market. 

Fusion  Pot  (see  Fig.  3). — On  the  laboratory  scale  the  pot  is  best 
made  of  copper  which,  on  account  of  its  good  conductivity,  leads 
to  a  considerable  saving  of  gas,  and  is  therefore  very  cheap  to  work 
with.  The  same  remarks  that  were  made  as  to  the  moving  parts 
of  the  apparatus  in  the  case  of  the  sulphonating  vessel  apply  in  the 
present  case  (p.  5).  The  high  melting-point  of  the  naphthol 
renders  it  necessary  for  the  stirrer  to  scrape  the  entire  surface  of  the 


8 


INTERMEDIATE  PRODUCTS 


vessel  (see  figure).  The  thermometer  dips  into  a  narrow  copper 
tube  which  is  brazed  together  at  the  bottom  and  filled  with  lubricating 
oil  to  a  sufficient  extent  to  ensure  that  at  least  10  cm.  of  the  ther- 
mometer is  covered.  Another  good  plan  is  to  have  the  thermometer 
fitted  into  the  hollow  spindle  of  the  stirrer. 
Reaction  : 


+Na2SO3+H2O 


+Na2S04) 


(Side  reaction  : 


2OO 

NaO 


60  c.cs.  H2O, 


In  order  to  ensure  that  the  caustic  soda  and  the  sodium  salt  shall 

fuse  together  readily  it  is 
necessary  that  the  latter  be 
as  finely  powdered  as  pos- 
sible. In  the  laboratory 
this  is  most  conveniently 
effected  by  grinding  the 
coarse  salt  in  a  powerful 
coffee  mill. 

The  fusion  pot  is  now 
placed  directly  on  a  small 
Fletcher  burner  and  is 
charged  with  200  gms. 
solid  caustic  soda,  free  from 
chlorate,  in  coarse  lumps 
and  60  c.cs.  water.  If  the 
caustic  contains  chlorate 
the  yield  will  be  dimin- 
ished, and  there  is  also  very 
great  risk  of  explosion. 
The  caustic  soda  is  melted 
to  a  clear  liquid  with  the 
aid  of  a  full  flame  and  the 
temperature  raised  by  de- 
grees to  270°  ;  the  foaming 


which  occurs  during  the 
heating  ceases  at  that  tem- 
perature. The  powdered 
sodium  salt  is  now  added 


FIG.  3. — Fusion  pot  for  /?-naphthol. 


continuously,  a  spoonful  at  a  time  with  stirring,  the  temperature  being 


SULPHONATIONS  9 

allowed  to  rise  slowly  to  290°.  The  dry  sodium  salt  will  be  seen  to 
disappear  slowly,  giving  place  to  the  dark,  mobile,  and  glistening 
sodium  naphtholate.  Owing  to  the  fluid  character  of  the  naphtholate 
it  is  now  possible  to  add  considerably  more  sodium  salt  than  is  given  300  gms. 
in  most  recipes.  In  the  laboratory  it  is  quite  easy  to  work  with  ^'salt- 
ii  parts  of  sodium  salt  for  each  part  of  caustic  soda  used.  On  the 
works  scale,  given  suitably  constructed  apparatus  and  adequate 
heating,  e.g.  with  generator  gas,  it  is  possible  to  add  2*8  parts  of 
salt  to  each  part  of  caustic  without  any  danger  of  burning,  or  of  the 
mass  becoming  too  thick.  About  half  the  j8-salt  (150  gms.)  should 
have  been  added  by  the  time  the  temperature  has  reached  290°. 
The  temperature  is  now  raised  cautiously  to  300°,  then,  when  three- 
quarters  of  the  salt  (225  gms.)  have  been  added,  to  305°,  and,  finally, 
when  it  has  all  been  added,  to  318°.  On  no  account  must  this  latter 
temperature  be  exceeded.  The  melt  attains  by  degrees  a  gritty  con- 
sistency due  to  the  separation  of  sodium  sulphite,  and  the  caustic 
soda  is  slowly  displaced  by  the  naphtholate.  The  whole  melt  is 
now  kept  for  15  minutes  at  318°  with  continuous  stirring,  taking 
care  that  no  overheating  occurs.  The  complete  process,  from  the 
time  of  the  first  addition,  should  occupy  about  one  hour  ;  if  the  salt 
be  added  too  quickly  some  charring  will  occur  with  inevitable 
lessening  of  the  yield. 

The  contents  of  the  fusion  pot  are  now  poured  on  to  a  tin  tray. 
As  soon  as  it  is  cold  the  product  is  broken  up  and  returned  to  the 
pot,  together  with  J  litre  of  water.  On  warming  gently  a  con- 
siderable portion  goes  into  solution,  but  a  crust  of  sodium  sulphite 
always  remains  behind  ;  the  solution  is  therefore  poured  off  and 
fresh  water  added  until  the  entire  melt  is  in  solution.  It  should  not 
be  necessary  to  use  more  than  2  litres  for  this  purpose.  The 
solutions  are  then  mixed  and  heated  to  boiling  over  a  Fletcher 
burner  and  treated  with  50  %  sulphuric  acid  until  practically  no 
reaction  is  given  with  thiazole  paper  ;  after  cooling  somewhat  the 
liquid  is  sucked  into  a  pre-warmed  flask  through  a  large  porcelain 
filter-funnel  ("  Nutsche  ").  The  volume  of  the  neutral  and  filtered 
solution  should  be  about  3  litres,  and  its  colour  not  more  than  faint 
yellow. 

This  solution  is  now  heated  to  boiling,  and,  whilst  stirring  well, 
sufficient  50  %  sulphuric  acid  is  added  until  litmus  paper  is  strongly 
reddened.  There  will  be  no  odour  of  sulphurous  acid,  as  j8-naphthol 
is  insoluble  in  neutral  sodium  sulphite  in  presence  of  a  little  bisulphite, 
and  therefore  separates  out,  at  first  as  an  oil,  which  immediately 
solidifies.  The  precipitated  substance  may  be  filtered  off  after  an 


io  INTERMEDIATE  PRODUCTS 

hour  or  so  without  losing  more  than  a  trace  of  naphthol,  using  a 
cotton  filter-cloth,  and  washing  the  product  carefully  with  water. 
Before  distillation  the  naphthol  should  be  dried  at  a  low  temperature 
either  in  a  vacuum  drying  chest  or  in  a  warm  room  ;  if  it  is  heated 
too  much  it  melts  and  sublimes. 

The  yield  of  dried  crude  naphthol  from  300  gms.  p-salt  is  about 
150  gms.  (93  %  pure),  and  of  distilled  product  135  gms.  M.p.  122°. 

The  crude  product  is  quite  adequate  for  most  purposes,  but  for 
sale  it  must  be  carefully  purified  owing  to  the  very  high  standard 
required.  At  the  present  day  vacuum  distillation  only  is  made 
use  of  (q.v.),  but  for  many  years  the  B.A.S.F.,  for  example,  dis- 
tilled all  their  naphthol  with  super-heated  steam  in  order  to  get  a 
really  first-class  product.  (The  important  method  of  steam- distilla- 
tion will  be  discussed  later.) 

Notes  on  Works  Technique  and  Practice. — The  sulphonation  of 
naphthalene  is  always  carried  out  on  the  large  scale  in  huge  cast-iron 
vessels  holding  1000  to  3000  litres.  They  are  heated  either  with 
direct  (generator)  gas  heating,  or  by  means  of  a  steam  jacket  (double- 
(See  Plate  bottom),  which  must  be  capable  of  withstanding  at  least  6  atmo- 
spheres in  order  to  attain  the  requisite  temperature  of  174°. 

The  precipitation  of  the  naphthalene  salt  is  effected  in  wooden 
vats  (Plate  VII.).  The  filtration  is  done  in  wooden  presses,  and  the 
salt  wrapped  in  hair  cloths,  after  which  it  is  pressed  in  hydraulic 
presses  at  about  250  atmospheres.  Hydraulic  accumulators  are  not 
to  be  recommended  for  this  purpose,  as  the  rapid  increase  in  pressure 
invariably  bursts  the  cloths.  Small  pumps,  such  as  that  shown  in 
Plate  III.,  however,  are  very  suitable  for  the  purpose,  as  they  cause 
a  gradual  increase  in  pressure,  and  cut  out  automatically  as  soon  as 
the  maximum  has  been  reached. 

The  melt  is  carried  out  in  flat  cast-iron  pans  with  a  plough 
stirrer,  the  heating  being  either  by  means  of  coal  or,  better,  by 
generator-gas,  the  waste  heat,  as  already  mentioned,  being  utilized 
for  drying  the  naphthalene  salt  in  drying  ovens. 


Naphthylaminetrisulphonic    acid     1:8:3:6    and     Amino- 
naphtholdisulphonic  acid  1:8:3:6  (H-acid). 

Reaction  : 


SO3H 


SULPHONATIONS 


ii 


SOoH     NO< 


3 


S03H     NH 

xi 


OH     NH, 


S03H 


SCXH 


In  order  to  carry  the  sulphonation  beyond  the  beta-sulphonic 
acid  stage  it  is  necessary  to  make  use  of  a  considerable  excess  of 
sulphuric  acid  ;  the  acids  so  obtained 
are  then  usually  cooled  and  nitrated. 
If  too  little  sulphuric  be  used  thick 
and  viscous  products  are  obtained 
after  the  sulphonation,  which  render 
stirring  impossible.  The  excess  of 
sulphuric  acid  acts  as  a  diluent,  but 
may  be  reduced  somewhat  on  a 
works  scale  as  more  powerful  stirring 
appliances  are  available. 

The  apparatus  required  is  the 
same  as  that  described  for  the  pre- 
paration of  naphthalene  sulphonic 
acid,  or  as  shown  in  Fig.  4.  It 
.consists  of  an  iron  vessel  which  has, 
besides  the  large  central  opening, 
two  smaller  necks  through  which  the 
thermometer  and  funnel  are  inserted. 
The  trouble  with  sulphur  trioxide 
vapours  is  almost  completely  avoided 
in  this  manner,  and,  in  addition,  the 
vessel  can  never  crack  when  placed 
in  cold  water,  which  would,  of 
course,  be  very  dangerous  when 
using  oleum. 

We  start  with  2  gram-molecules 

of   naphthalene,    which,    as    in   the    , 

,   ,  .  r  t    ,     *        .      FIG.  4. — Autogenously  welded  sul- 

Sulphonation       for      ^-naphthol,       IS       phonating  pot  for  use  with  oleum. 

heated  to  165°.     For  the  sulphona-      suita!?!e  also  for  the  preparation 

,        ,    ,       .          .  i       ot  aniline,  etc. 
tion,  however,  100  %  sulphuric  acid 

is  used,  not  93  %,  so  as  to  avoid  wasting  any  sulphuric  anhydride 
afterwards  by  combination  with  the  water. 

If  we  used,  for  example,  instead  of  the  28o-gm.  monohydrate 
the  same  weight  of  93  %  acid,  then  we  should  by  this  means  be 
introducing  18  gms.  (=i  mol.)  water  ^into  the  reaction  mixture 
at  the  very  beginning,  which  alone,  in  order  to  obtain  any  trisulphonic 


256  gms. 
Naphthalene. 


12  INTERMEDIATE   PRODUCTS 

acid,  would   require  the  addition  of    i  mol.  SO3,  or  200  gms.  of 
40  %  fuming  acid,  which  would  thus  be  completely  wasted, 
280  gms.  28°  Gms.  of  monohydrate  are  added  cautiously  drop  by  drop 

H2SO4  to  the  naphthalene  melt,  which  is  kept  vigorously  stirred.     It  is 

inadvisable  to  work  too  quickly,  as  otherwise  local  cooling  may  occur, 
which  favours  the  formation  of  the  a- acid.  Under  the  conditions 
given  the  addition  should  occupy  about  half  an  hour  ;  the  mixture 
becomes  very  hot,  differing  thus  from  the  sulphonation,  for  which 
reason  only  very  slight  heating  is  required,  or  none  at  all.  The 
cooling  due  to  radiation  compensates  almost  exactly  for  the  heating 
due  to  the  chemical  reaction.  When  the  mixture  is  complete,  the 
product  is  kept  for  a  further  hour  at  165°,  and  is  then  cooled  down  by 
placing  the  pot  in  ice-water  until  the  contents  show  a  temperature 
of  75°.  It  is  inadvisable  to  cool  below  this  temperature,  as  otherwise 
the  contents  are  liable  to  solidify,  and  can  then  no  longer  be  stirred. 
The  further  sulphonation  with  fuming  sulphuric  acid  leads  to  a 
whole  series  of  isomers  which  are  only  partially  known.  By  keeping 
exactly,  however,  to  certain  definite  conditions,  it  is  possible  so  to 
favour  the  formation  of  the  1:3:6  acid,  that  approximately  60  % 
of  the  desired  compound  may  be  obtained.  In  order  to  obtain  the 
trisulphonic  acid  of  naphthalene, #t  least  so  much  sulphuric  anhydride^ 
must  be  used  that  no  water  will  occur  in  the  equation  at  the  end  of 
the  reaction.  In  other  words,  at  the  end  of  the  process  only  mono- 
hydrate  or  a  very  weak  fuming  sulphuric  acid  should  be  present  in 
the  product  besides  the  trisulphonic  acid.  If  this  necessary  minimum 
quantity  of  SO3  is  not  used,  it  will  be  impossible  to  convert  all  the 
naphthalene  into  the  trisulphonated  derivative,  no  matter  how  long 
it  is  heated,  and  the  yield  will  be  diminished  by  an  amount  equal 
to  four  times  the  quantity  of  the  insufficiently  sulphonated  substance. 
This  affords  an  example  of  a  phenomenon  which  is  frequently 
observed  in  applied  organic  chemistry  :  — 

Slight  variations  from  the  optimum  conditions  will  cause  losses 
which,  apparently,  are  quite  out  of  proportion  to  the  error  which  has 
been  made. 

No  harm,  however,  will  be  caused  by  an  excess  of  sulphuric 
anhydride,  so  long  as  this  is  kept  within  reasonable  limits  ;  in 
recognition  of  this  fact  an  excess  of  about  10-15  %  of  SO3  is  taken. 
Commercial  fuming  sulphuric  acid  contains  almost  invariably  too 
little  anhydride,  owing  to  the  absorption  of  a  little  water  whilst 
transferring  to  smaller  vessels.  As  a  simple  calculation  shows, 
however,  very  slight  quantities  of  water  reduce  the  SO3  content  to 
quite  an  extraordinary  degree.  The  oleum  which  is  used  in  the 


PLATE   II. 


o 

ex, 

60 

g 

+3 


—    w 

c  « 


r 

o 

^On 
3 


II 


a  o 

«•£ 


SULPHONATIONS  13 

works  has  a  much  more  constant  composition,  as  it  is  less  easy  for 
water  to  be  absorbed  by  the  large  quantities  of  acid  dealt  with.  To 
a  great  extent  the  concentration  of  the  oleum  used  depends  upon 
the  personal  preferences  of  the  works  chemist  ;  sulphuric  acid  con- 
taining anything  from  30-60  %  SO3  may  be  used  without  hesitation, 
but  the  latter  strength  (60  %)  is  recommended,  as  it  remains  liquid 
at  lower  temperatures  and  does  not  require  any  troublesome  heating. 

It  is  very  important  that  the  temperature  at  which  naphthalene- 
monosulphonic  acid  and  sulphur  trioxide  are  mixed  should  be  as 
low  as  possible,  or  else  losses  are  caused  owing  to  SO3  distilling  off, 
and  to  charring.  As  soon  as  the  temperature  of  the  monosulphonic 
acid  has  fallen  to  75°,  120  gms.  of  monohydrate  are  mixed  with  120  gms. 
the  product  in  order  to  prevent  the  contents  of  the  vessel  from  ?J^  oK 
solidifying  on  further  cooling.  The  mixture  is  allowed  to  cool 
with  continuous  stirring  to  50°,  and  the  cautious  addition  of  the 
oleum  is  then  begun.  At  first  the  mixture  heats  up  very  strongly,  900  gms. 
for  which  reason  it  is  necessary  to  start  very  slowly.  As  soon  as  s°3  (6o 
the  water  produced  in  the  reaction  has  been  used  up,  it  becomes 
possible  to  work  more  quickly,  and,  finally,  the  remainder  of  the  acid 
may  be  run  in  during  the  course  of  a  few  minutes.  The  addition  of 
the  oleum  will  occupy  in  the  laboratory  from  half  to  one  and  a 
half  hours,  according  to  the  amount  of  cooling.  The  mixture  is  now 
heated  to  165°,  and  kept  at  this  temperature  for  6  hours  with  slow, 
continuous  stirring.  This  length  of  time  must  be  strictly  adhered 
to,  although,  as  may  easily  be  observed,  the  odour  of  SO3  will  have 
disappeared  after  half  an  hour.  During  the  slow  heating,  however, 
transformations  take  place  which  have  been  little  investigated,  but 
which,  without  any  doubt,  lead  towards  the  formation  of  the  desired 
trisulphonic  acid. 

We  now  convert  the  trisulphonic  acid  so  obtained,  without 
isolating  it,  into  the  nitro-trisulphonic  acid  1:3:6:8.  The  nitra- 
tion of  the  mixture  of  the  numerous  isomers  leads,  of  course,  to  the 
formation  of  quite  a  number  of  nitrosulphonic  acids  which  must 
be  regarded  as  so  much  ballast.  Besides  the  isomers,  however, 
oxidation  products  are  also  formed  which  affect  the  yield.  In  the 
laboratory  the  nitration  is  done  in  the  same  vessel  in  which  the 
sulphonation  is  carried  out,  placing  it  for  this  purpose  in  ice-water. 
For  two  molecules  naphthalene,  two  molecules  nitric  acid  are  required, 
preferably  as  60  %  HNO3  (40°  Be.).  This  quantity  of  acid  is  added 
slowly  through  the  dropping  funnel,  temperature  about  15-20°. 
In  the  laboratory  the  nitration  should  occupy  about  3  hours. 
After  all  the  nitric  acid  has  been  run  in,  the  mixture  is  allowed  to 


H  INTERMEDIATE   PRODUCTS 

stand  at  25°  for  at  least  10  hours,  and  is  then  poured  into  3  litres 
of  water  ;  volumes  of  nitrous  fumes  are  given  off  and  the  aqueous 
solution  heats  up  to  70-80°. 

There  are  a  number  of  methods  for  isolating  the  nitro-naphthalene 
trisulphonic  acid  or  the  naphthylamine  trisulphonic  acid.  Most  of 
these,  however,  are  devoid  of  technical  interest  owing  to  various 
disadvantages.  It  would  appear  to  be  a  simple  matter  to  isolate 
the  nitro-naphthalene  trisulphonic  acid,  as  about  95  %  of  it  separates 
out  in  the  form  of  its  acid  sodium  salt  on  the  addition  of  common 
salt ;  after  standing  for  some  time  this  is  filtered  off,  the  resultant 
cakes  are  pressed  by  hydraulic  means,  dissolved  in  soda,  and  then 
reduced  in  faintly  acid  solution.  Although  this  process  appears 
quite  simple  at  first  sight,  and  offers  the  attraction  of  recovering  the 
sulphuric  acid  by  avoiding  the  liming-out  process,  it  is,  nevertheless, 
impossible  to  carry  out  owing  to  the  almost  insuperable  difficulties 
involved  in  dealing  with  the  acid  solutions.  All  the  apparatus, 
filter-cloths,  etc.,  are  rapidly  destroyed  by  the  24  %  hydrochloric 
acid,  repairs  use  up  a  great  deal  of  material,  and  good  workmen 
refuse  after  a  time  to  take  charge  of  such  unpleasant  operations. 
In  addition,  quite  slight  alterations  in  the  composition  of  the  nitrating 
liquid  may  prevent  the  complete  separation  of  the  nitro  acid.  In 
the  laboratory,  however,  this  method  is  quite  suitable  for  obtaining 
quickly  a  supply  of  pure  H-acid. 

Again,  the  original  process  of  D.  R.  P.  56058  is  not  a  practical 
one,  as,  according  to  this  method,  the  entire  solution  of  the  nitro- 
product  is  reduced  with  iron.  The  large  quantities  of  gypsum  mixed 
with  the  still  larger  quantities  of  iron  hydroxide  which  are  formed 
on  liming  the  entire  liquid  make  this  process  very  unprofitable ; 
further,  the  huge  quantities  of  water  which  would  have  to  be  evapo- 
rated off  would  alone  suffice  to  settle  its  fate. 

The  best  and  most  generally  used  process  consists  in  first 
removing  the  excess  of  sulphuric  acid  by  means  of  lime,  and  then 
reducing  the  sodium  salt.  The  first  advantage  in  so  doing  is  that 
the  alkaline-earth  or  alkali  salts  of  any  aromatic  nitrosulphonic  acid 
can  be  reduced  in  neutral  solution  ;  this  is  the  same  principle  that 
has  been  made  use  of  for  a  very  long  time  for  the  preparation  of 
aniline.  During  the  neutral,  or  more  accurately  faintly  acid  reduction 
of  the  product  in  question,  only  quite  slight  quantities  of  iron  go 
into  solution,  and  the  chief  amount  of  the  iron  oxide  appears  in  the 
form  of  the  black  ferroso-ferric  oxide  which,  owing  to  its  small 
bulk  and  excellent  filtering  qualities,  shows  obvious  advantages 
over  the  hydrated  iron  oxide.  The  quality  of  the  iron  used  is  a 


SULPHONATIONS  15 

very  important  matter,  and  failures  during  the  neutral  reduction 
are,  in  most  cases,  due  to  the  use  of  poor  quality  iron  ;  only  grey 
cast-iron  is  suitable,  and  neither  raw  iron,  steel,  nor  wrought  iron 
should  be  used,  as  under  the  conditions  which  we  have  chosen, 
they  exert  no  reducing  action. 

The  removal  of  the  excess  of  sulphuric  acid  may  be  effected  by 
the  use  either  of  slaked  lime  or  of  pure,  finely  powdered  chalk.  It 
will  be  found  that  calcium  carbonate  is  the  most  convenient,  as  it 
gives  a  much  more  compact  and  easily  filterable  gypsum.  It  has, 
however,  the  disadvantage  that  the  carbon  dioxide  evolved  may  lead 
to  frothing- over,  but  this  can  be  avoided  by  an  experienced  workman. 
It  is,  of  course,  possible  to  recover  the  carbonic  acid,  but  a  com- 
pressing plant  for  carbon  dioxide  presupposes,  in  this  case,  a  very 
well- organized  factory  which  is  not  afraid  of  expending  money  on 
plant  and  can,  in  addition,  make  use  of  the  gas  for  the  production 
of  salicylic  or  o-cresotinic  acids. 

The  decomposition  of  the  sulphonic  acids  is  always  carried  out 
in  conjunction  with  the  conversion  into  the  sodium  salt ;    this  is 
done  by  the  addition  of  the  calculated  quantity  of  Glauber  salt  to 
the  liquor  which  is  to  be  limed.     The  resulting  calcium  salts  of  the 
sulphonic  acids  immediately  react  with  the  Glauber  salt  to  give  the 
sodium  salt  and  gypsum.     Factories  which  make  formic  acid  have 
such  cheap  Glauber  salt  at  their  disposal  that  the  saving  is  very 
considerable  in  comparison  with  soda.     Three  molecules  (450  gms.)  450  gms. 
of  crude  anhydrous  Glauber  salt  are  first  added  to  the  sulphuric  Glaubersalt- 
acid  solution,  and    then  finely  powdered  limestone  is  added    by 
degrees,  with  good  stirring.     About  the  same  weight  of  limestone 
is  required  as  of  the  sulphuric  acid,  since  both  compounds  have 
almost  the  same  molecular  weight.     We  require,  therefore,  about 
1300  gms.  limestone  or  chalk,  corresponding  to  the  1300  gms.  of  1300  gms. 
sulphuric  acid  (oleum  and  monohydrate)  which  was  taken. 

The  vessel  in  which  this  is  carried  out  is  a  large  glass  cylinder 
holding  5  litres,  provided  with  a  glass  stirrer  of  similar  shape  to 
that  used  for  the  sulphonation.  It  is  advisable  to  calibrate  the 
vessel  beforehand,  and  to  paint  on  it  a  scale  showing  every  half-litre  ; 
small  trifles  like  this  facilitate  the  work  in  the  laboratory  to  a  surprising 
degree,  besides  training  the  eye  (Fig.  21). 

The  addition  of  the  carbonate  (lime-paste  may  also  be  used) 
must  be  made  very  cautiously  ;  any  excess  must  be  avoided,  particu- 
larly where  slaked  lime  is  used,  as  the  nitro  acids  are,  in  general, 
sensitive  to  alkali.  As  soon  as  the  mineral  acid  has  been  used  up, 
the  pale  yellow  colour  of  the  paste  changes  to  a  strong  yellow,  thus 


16  INTERMEDIATE   PRODUCTS 

indicating  the  end  of  the  liming  ;  the  gypsum  renders  the  mass  so 
thick  that  it  becomes  extremely  difficult  to  stir,  but  on  further 
stirring  the  paste  becomes  thinner,  so  that  there  is  no  difficulty  in 
filtering.  For  this  large  quantity  of  gypsum,  about  three  large 
porcelain  suction  filters  are  required,  using  either  paper  or  cotton 
filters.  The  gypsum  should  be  kneaded  with  a  big  spatula,  and 
will  then  be  found  to  shrink  together  to  a  remarkable  degree.  After 
the  precipitate  has  been  well  pressed  down,  it  is  washed  out  carefully 
with  cold  water,  filling  up  all  the  cracks  at  once.  It  is  quite  easy, 
with  thorough  washing,  to  keep  the  total  volume  of  liquid  below 
5  litres  ;  in  passing  it  may  be  noted  that  there  is  no  point  in  carrying 
the  washing  process  too  far.  The  colour  of  the  sodium  salts  of  the 
nitro  acids  is  so  intense  that  at  least  10  litres  of  washing  water  are 
required  before  a  colourless  filtrate  is  obtained.  In  cases  where 
uncertainty  is  felt  as  to  this  process,  it  is  best  to  wash  out  with  about 
a  litre  of  water,  tip  the  precipitate  again  into  the  stirring  vessel, 
and  then  to  paste  up  the  gypsum  carefully  with  3  litres  of  water  ; 
it  is  then  filtered  off  again  as  described  above,  and  washed  out  with 
a  little  water.  Any  rise  of  temperature  above  50°  must  be  avoided 
as  far  as  possible,  particularly  when  the  liming  out  is  done  with 
slaked  lime. 

It  is  not  possible  to  evaporate  down  the  solution  of  the  sodium 
salts  of  the  various  nitro-naphthalene  trisulphonic  acids,  as  these 
are  easily  decomposed.  It  therefore  becomes  necessary  to  reduce 
the  whole  solution,  which  requires,  of  course,  very  large  reduction 
vessels. 

The  reduction  of  the  nitro-naphthalene  trisulphonic  acid  is 
such  a  typical  example  of  this  kind  of  reaction  that  it  will  be  as  well 
to  describe  it  in  some  detail.  It  must  be  carried  out  at  the  boiling- 
point,  as  in  all  reductions  of  this  type,  or  else  azoxy  compounds  are 
formed  which  cannot  be  reduced  to  the  amino  compound,  or  only 
with  great  difficulty. 

The  apparatus  required  for  this  reaction  consists  of  a  capacious 
sheet-iron  pot,  holding  at  least  4  litres,  and  provided  with  a  pro- 
peller stirrer  (which  can  be  easily  made  by  any  tinsmith),  by  means 
of  which  it  is  possible  to  keep  the  iron  used  in  the  reaction  in  con- 
tinuous motion.  The  propeller  blades  soon  get  used  up,  so  that 
they  are  best  fixed  to  the  end  of  the  stirring  rod  by  simple  riveting. 
(See  Fig.  5,  p.  17).  If  no  propeller  agitator  is  available,  a  stirrer 
of  the  form  used  for  the  sulphonation  of  naphthalene  to  the  /3-acid 
may  be  employed  if  due  care  be  taken.  The  important  point  to 
notice  is  that  the  iron  powder  must  not  He  at  the  bottom  of  the  pot, 


SULPHONATIONS 


but  must  be  kept  swirling  round.  The  iron  pot  should  be  made 
from  lead-lined  iron  plate  to  prevent  it  from  rusting  too  quickly  ; 
further,  to  prevent  it  from  leaking,  it  should  be  lapped. 

The  pot  is  placed  on  a  ring  burner  and  filled  with  300  gms.   300  gms. 
sifted  iron  turnings  and  about  half  a  litre  of  water.     To  these  are   ^oc'c.  40 
added  20  c.c.  of  acetic  acid  (40  %),  and  the  mixture  is  then  boiled  Acetic  acid, 
up  well  with  good  stirring.     In  technical  language  the  iron  becomes  *  '  Water- 
"  etched."      Oxide,  oil,  , 

and     so      on     are     re-  m 

moved  in  this  manner, 
and  the  iron  converted 
into  the  desired  active 
form.  Meanwhile,  the 
solution  of  the  nitro- 
naphthalene  trisulphonic 
acid  is  made  just  acid  to 
Congo  with  dilute  sul- 
phuric acid.  It  is  also 
possible  to  use  the  much 
cheaper  sulphuric  acid 
in  place  of  the  expensive 
acetic  acid  for  "  etching  " 
the  iron,  but  the  yield 
of  naphthylamine  trisul- 
phonic acid  is  affected 
unfavourably  by  it,  being 
reduced  by  10-20  %. 
It  is  therefore  strongly 
desirable  to  reduce  in 
acetic  acid  solution.  In 

,1  r     <.u  FIG.  5. — Apparatus  with  propeller-stirrer   for   re- 

the  case  of  Other  ammo  d5uctio£s  by  Bechamp-Brimmeyr  method. 

acids,  such  as  Cleve  and 

naphthylamine  sulphonic  acids    1:8  and   1:5,  it  appears  to  be  less 

important  whether  acetic  acid  or  mineral  acid  be  used. 

As  soon  as  everything  is  ready,  the  iron  turnings  are  boiled  up 
for  five  minutes,  the  nitro  acid  made  faintly  acid  to  Congo,  and  the 
latter  solution  is  then  allowed  to  drop  in  slowly  through  a  dropping 
funnel,  exactly  as  in  the  case  of  the  sulphonation  of  naphthalene. 
It  is  absolutely  essential  that  the  mixture  be  kept  boiling  vigorously 
the  whole  time.  A  drop  placed  on  filter  paper  should  show  no 
coloration,  as  this  would  indicate  the  presence  of  azoxy  compounds 
which  have  a  harmful  action.  The  rate  of  reduction  can  be  so 


i8  INTERMEDIATE   PRODUCTS 

arranged  that  the  whole  solution  is  run  in  during  one  hour.  A  con- 
siderable quantity  of  water,  of  course,  evaporates  off,  so  that  the 
volume  of  the  reduction  liquid  becomes  diminished  to  two-thirds  or 
less.  When  all  has  been  added,  the  whole  is  boiled  up  with  con- 
tinuous stirring  for  another  quarter  of  an  hour,  and  is  then  allowed 
to  cool  somewhat.  With  good  quality  iron  it  may  be  noticed  that 
hydrogen  is  evolved  vigorously  long  after  the  reduction  is  complete, 
showing  that  cast-iron  is  attacked  by  water,  even  in  the  presence  of 
10  gms.  iron  salts.  10  Gms.  of  calcined  soda  are  then  sprinkled  into  the 

Na2CO3.         liquid  with  a  teaspoon,  until   red  litmus   paper  is  turned  strongly 
blue.     (Caution  :  The  solution  readily  froths  over  !) 

A  test  should  also  be  made  with  sodium  sulphide  upon  filter 
paper  to  ascertain  whether  all  the  iron  has  been  precipitated.  It 
is  then  filtered  through  a  suction  filter,  the  iron  oxide  remaining  as 
a  black  velvety  precipitate  on  the  "  nutsch,"  whilst  the  unused  iron 
remains  at  the  bottom  of  the  pot ;  the  latter  is  then  rinsed  out  into 
the  filter  and  well  washed.  In  the  works  the  iron  powder  is  allowed 
to  remain  in  the  reduction  vessel,  and  is  then  used  for  the  next 
operation.  A  good  reduction  liquor  of  the  amino-naphthalene 
trisulphonic  acid  should  be  colourless  or  pale  yellow,  and  in  no 
case  should  it  be  reddish  or  brown.  In  the  laboratory  the  solution 
is  placed  in  a  good  porcelain  dish,  and  is  then  evaporated  down  with 
direct  heating  to  about  i  J  litres. 

Formerly,  it  was  the  practice  to  melt  up  the  product  straight 
away  to  H-acid.  This  method,  however,  is  rather  barbaric,  as  by 
so  doing  not  only  is  the  required  amino-acid  melted  up,  but  all  the 
isomers  as  well.  The  yield  was  accordingly  very  unsatisfactory, 
about  80  %  of  theory  of  the  total  acids  being  obtained  from  one 
molecule  naphthalene,  which  would  use  up  56  gms.  of  sodium 
nitrite.  On  melting  the  product  it  was  not  possible  to  obtain  more 
than  55-60  %  of  theory  of  H-acid,  and  the  product  was  very  impure. 
It  was  therefore  a  distinct  step  forward  when  it  became  the  practice 
to  isolate  the  naphthylamine  trisulphonic  acid  first,  and  then  to  melt 
the  purified  acid.  At  the  present  day  all  the  works  use  this 
process,  some  of  them  recrystallizing  the  isolated  acid  from  water. 

In  order  to  isolate  the  naphthylamine  trisulphonic  acid  1:8:3:6 

the  evaporated  solution  is  placed  in  a  glass  vessel  of  2  litres  capacity. 

zoo  gms.         20°   gms-  °f   common  salt  are  added,  and  then,  with  continuous 

Salt.  stirring,  sufficient  concentrated  sulphuric  acid  to  make  the  solution 

ca.  80  gms.      strongly  acid  to  Congo  paper.     After  a  short  interval,  the  solution 

conc.H2SO4.  r    «          1.  i./-  .  1  •  r    i  -j        j*  1^ 

practically  solidifies  owing  to  the  separation  of  the  acid  sodium  salt 

of  the  sulphonic  acid.     Stirring,  however,  must  still  be  continued, 


SULPHONATIONS  19 

and,  as  is  so  often  the  case,  under  the  influence  of  the  continuous 
movement  the  pasty  mass  finally  becomes  quite  fluid  again.  After 
standing  for  at  least  10 'minutes,  the  precipitate  is  filtered  off,  and 
the  vessel  finally  rinsed  out  with  a  portion  of  the  filtrate.  The 
precipitate  must  be  well  pressed  down,  and  should  be  pure  white. 
Its  weight  is  about  700  gms.,  and  corresponds  to  at  least  70  gms. 
sodium  nitrite.  The  mother-liquor  would  also  use  up  about  30 
gms.  of  nitrite,  but  is  quite  valueless.  It  is  noteworthy  that  during 
the  process  of  purification  only  the  desired  sulphonic  acid  is  obtained 
together  with  quite  a  small  quantity  of  isomers. 

On  melting  the  amino  acid  in  question  with  alkali  H-acid  is  pro- 
duced (aminonaphthol-disulphonic  acid  1:8:3:6),  which  is  the  most 
important  dye  intermediate  of  the  kind,  and  is  a  good  example 
of  this  type  of  operation. 

To  obtain  H-acid  in  good  yield  the  temperature  must  not 
exceed  190°,  and  the  caustic  soda  used  should  be  at  least  30  %. 
The  following  charge  will  be  found  convenient  for  a  laboratory 
melt  :— 

28  nitrite  naphthylamine  tri sulphonic  acid = about  280  gms.  28  Nitrite 

/  trisulph. 

damp  presscake.  acid. 

130  gms.  caustic  soda.  J3°  gms- 

1 30  gms .  water.  130  gni. 

Water.  Total 

This  operation  is  carried  out  in  an  autoclave,  a  piece  of  apparatus  wt.  about 
which  plays  such  an  important  part  both  in  the  laboratory  and  in  the  54°  gmSt 
factory,  that  a  special  chapter  is  devoted  to  it  (q.v.).  It  is  charged 
with  the  given  quantities  of  materials,  and  the  melt  is  then  carried  out 
at  178-180°  during  8  hours  with  continuous  stirring,  the  pressure 
being  about  7  atmospheres.  After  cooling,  the  autoclave  is  opened, 
any  residual  pressure  being  let  of!  first  by  means  of  the  valve.  If  the 
melt  has  been  carried  out  correctly,  the  product  will  be  of  a  somewhat 
dull  dirty-yellow  colour  ;  if  it  is  too  light,  the  melt  was  too  short ; 
whilst  if  it  is  brown  and  smells  very  strongly  of  ammonia,  the  melt 
has  been  carried  too  far.  At  the  same  time,  however,  a  certain 
amount  of  ammonia  is  always  split  off  even  with  the  most  careful 
fusion. 

The  product  obtained  forms  a  syrupy  mass  which  is  mixed 
with  granular  crystals  of  anhydrous  sodium  sulphite,  and  after 
introducing  into  a  stoneware  jar  of  2  litres  capacity,  it  is  diluted 
with  i  litre  of  water  and  acidified  with  50  %  sulphuric  acid  until  it 
shows  a  strong  and  permanent  mineral  acid  reaction  with  Congo 
paper  ;  care  must  be  taken  not  to  be  deceived  by  the  action  of  the 


20  INTERMEDIATE  PRODUCTS 

free  sulphurous  acid  which  rapidly  evaporates  off  (fume-cupboard  !). 
The  aminonaphthol  disulphonic  acid  is  precipitated  in  the  form  of 
fine  white  crystals,  which  are  very  sparingly  soluble  in  a  concentrated 
solution  of  Glauber  salt.1 

It  is,  however,  preferable  to  allow  the  precipitate  to  stand 
for  a  few  hours,  to  ensure  that  the  separation  is  complete  ;  it 
is  then  filtered  off,  and  the  precipitate  washed  with  10  %  brine  to 
which  i  %  hydrochloric  acid  has  been  added.  Washing  must  not 
be  carried  on  too  long,  otherwise  some  H-acid  will  be  lost.  Finally, 
it  is  pressed  out  well  with  a  screw-press  and  dried  at  100°. 

The  yield  of  100  %  H-add  is  about  100  gms.,  or  approximately 
no  gms.  H-acid  of  86  %  purity.  (For  quantitative  estimation,  see 
Analytical  Section.) 

Notes  on  Works  Technique  and  Practice. — The  sulphonation  of 
naphthalene  to  the  trisulphonic  acid  is  nearly  always  carried  out  in 
steam-heated  cast-iron  boilers.  As  already  noted,  the  mass  heats 
up  strongly  on  the  addition  of  the  monohydrate,  and  still  more  with 
the  oleum,  so  that  on  the  large  scale  the  mixing  of  the  substances 
takes  considerably  longer  than  in  the  laboratory.  With  a  charge  of 
260  kgs.  of  naphthalene  the  preparation  of  the  monosulphonic 
acid  will  take  quite  i  J  hours,  even  with  the  most  careful  cooling,  and 
the  addition  of  about  1000  kgs.  of  oleum  will  occupy  more  than 
3  hours  if  one  is  to  avoid  the  loss  of  large  quantities  of  SO3  by 
volatilization  and  the  complete  oxidation  of  considerable  quantities 
of  naphthalene. 

By  the  use  of  a  steam-jacketed  vessel  it  is  easy  to  regulate  the 
temperature  by  allowing  cold  water  to  circulate  through  the 
jacket. 

To  save  time,  and  to  ensure  that  the  vessels  are  always  as  full 
as  possible,  the  nitration  is  carried  out  practically  exclusively  in  one 
special  vessel.  The  sulphonated  mass  is  forced  over  by  means  of 
compressed  air  through  a  pipe  into  a  nitrating  pot  that  may  have 
the  form,  for  instance,  given  in  Plate  II.  Cooling  is  carried  out  by 
means  of  water  or  ice,  or,  better  still,  by  means  of  a  cooling  coil 
through  which  brine  at  —15°  is  circulating.  In  the  latter  case  the 
vessel  stands  in  concentrated  salt  solution.  If  ice  is  used  it  is  a  good 
plan  to  add  some  salt  to  the  cooling  liquid,  and  at  the  same  time  to 
get  the  freezing  mixture  well  mixed  by  means  of  a  stream  of  air 
introduced  just  beneath  the  surface,  the  cooling  effect  being  thus 

1  Solubility  of  H-acid  : — 

at  18°  in  water 0*93     %. 

at  18°  in  10  %  NaCl          .          .       ..    ,      .  0-053%. 

at  i8°in  10  %NaCl+o'8  %  HC1      .          .  0*023  %. 


SULPHONATIONS  21 

made  more  rapid.  In  the  works,  owing  to  the  difficulty  in  cooling, 
the  nitration  is  rarely  carried  out  below  25°,  and  may  occupy  more 
than  8  hours.  It  must  be  noted  here,  however,  that  a  thermometer 
may  be  registering  only  25°  whilst  at  the  point  where  the  nitric  acid 
is  run  in  the  temperature  may  be  considerably  higher,  although  not 
shown  by  the  thermometer. 

In  a  well-conducted  factory  the  nitrous  fumes  given  off  on 
dilution  are,  for  the  most  part,  condensed  in  water  to  give  nitric 
acid  ;  for  this  purpose  a  fairly  large  plant  is  necessary,  consisting 
of  earthenware  pots,  filled  with  Guttmann  balls  or  Raschig  rings  (q.v.). 

The  liming-out  is  always  carried  out  in  wooden  vats,  as  shown 
in  Plate  VII.  The  gypsum  is  filtered  off  with  suction  or  under 
pressure,  and  more  recently  it  has  been  separated  with  considerable 
success  by  centrifuging.  The  centrifuges  (Plate  V.)  are  driven 
from  beneath,  and  usually  also  can  be  emptied  from  the  bottom. 
On  the  large  scale  they  are  made  up  to  i  J  metres  in  diameter,  and 
are  so  arranged  that  the  "  whizzed  "  gypsum,  mixed  with  relatively 
little  water,  can  be  emptied  direct  into  the  tip- waggons. 

The  reduction  of  the  large  quantities  of  liquid  also  offers  con- 
siderable difficulties.  The  reduction  vessels  consist  of  huge  wrought- 
iron  pots  such  as  are  shown  on  Plate  IV.  Owing  to  the  scouring 
action  of  the  iron,  the  bottom  of  the  vessel  must  either  be  made 
easily  removable,  e.g.  by  screwing  on  a  special  base-plate  that  can 
be  replaced  easily  when  it  gets  used  up,  or,  better,  the  bottom,  and 
if  necessary  the  whole  vessel,  is  lined  with  acid-proof  tiles.  After 
the  reduction  is  complete,  a  pipe  is  inserted  and  the  contents  blown 
over  by  compressed  air  into  the  filter-press.  The  turnings  are 
pulverized  in  ball- mills. 

The  evaporation  is  always  carried  out  in  multiple- effect  evapora- 
tors, triple- effect  evaporators,  similar  to  those  employed  in  the  beet- 
sugar  industry,  being  used  in  the  large  German  factories.  The 
saving  in  coal  as  compared  with  evaporation  under  ordinary  pressure 
is  about  80  % .  The  precipitation  and  isolation  of  the  naphthylamine 
trisulphonic  acid  require  exactly  the  same  apparatus  as  has  been 
described  for  j8-naphthalene  monosulphonic  acid  (see  Plates  III.  and 
VII.).  As  the  press-cakes,  pressed  at  250  atmospheres,  are  stone- 
hard  and  very  tough,  they  must  be  coarsely  ground  in  breakers 
provided  with  toothed  rollers,  before  being  melted.  At  the  same 
time  the  yield  of  titratable  naphthylamine  trisulphonic  acid  is 
determined  in  a  definite  portion.  The  melt  is  carried  out  in  auto- 
claves provided  with  a  manhole  cover,  thermometer- tube,  and  two 
manometers.  Two  reducing  valves  are  always  provided,  so  that 


22  INTERMEDIATE   PRODUCTS 

in  case  one  fails,  there  will  always  be  one  in  reserve.  (For  farther 
details  see  the  general  section  on  Autoclaves.)  The  so-called 
H-acid,  even  after  it  has  been  compressed  by  hydraulic  means,  still 
contains  a  large  proportion  of  water  (about  40  %).  In  the  moist 
state  it  cannot  be  stored  for  long,  as  it  rapidly  oxidizes,  and  it  is 
therefore  either  dissolved  and  the  titrated  solution  then  used  at 
once  in  another  portion  of  the  works,  or  more  usually  it  is  dried 
in  vacuo,  and  then  ground  up  to  the  consistency  of  a  fairly  fine 
gravel.  It  is  unwise  to  grind  it  too  finely,  as  this  increases  the  rate 
of  oxidation,  and  the  disintegrated  H-acid  dissolves  with  difficulty, 
a  sticky  paste  forming  on  the  sides  of  the  vats.  So  far  as  I  am  aware 
the  H-acid  in  nearly  all  factories  is  dried  to  allow  of  accurate  calcula- 
tion, as  is  the  case  with  all  similar  products.  Curiously  enough,  oh 
the  large  scale  the  precipitation  takes  much  longer  than  in  the  labora- 
tory. For  this  reason  the  liquid  must  be  allowed  to  stand  for  at 
least  12  hours  after  the  addition  of  the  acid,  as  otherwise  considerable 
quantities  of  H-acid  are  lost.  Many  other  cases  are  known  of  the 
slow  precipitation  of  difficultly  soluble  precipitates,  e.g.  benzidine 
disulphonic  acid,  gallamide,  gallic  acid,  etc.  Presumably  on  the 
large  scale  considerably  fewer  nuclei  for  crystallization  are  present, 
so  that  for  a  given  temperature  the  separation  of  large  quantities 
takes  a  much  longer  time. 

As  a  general  rule,  it  may  be  noted  that  the  melts  of  all  sulphonic 
acids  only  go  well  when  the  salt  content  of  the  starting  material  is  very 
slight ;  salt  is  practically  a  poison  for  alkali  fusions,  as  owing  to  its 
insolubility  in  caustic  soda  it  leads  to  scorching,  and  further  it  reduces 
the  solubility  of  the  resulting  sulphite  and  of  the  sulphonic  acid 
which  is  to  be  melted.  It  is  quite  possible  to  increase  the  yield  of 
amino-naphthol  sulphonic  acids  up  to  90  %  by  careful  attention  to 
all  the  essential  details.  Frequently  it  is  necessary  to  use  potassium 
hydroxide  in  place  of  the  cheaper  caustic  soda,  and  sometimes  the 
fusion  must  be  carried  out  in  open  vessels,  as  in  the  case  of  amino- 
naphthol  sulphonic  acid  1:8:4.  In  eacn  case  tne  most  favourable 
conditions  must  be  worked  out  first. 

The  caustic  soda  must  be  free  from  carbonate.  It  is  dissolved 
in  large  batches  and  made  up  to  50  % .  For  use  it  is  not  weighed  but 
is  measured  into  the  autoclaves  by  means  of  a  measuring  vessel. 
The  liquor  is  stirred  by  means  of  compressed  air  and,  owing  to 
the  danger  of  the  stock  solution  freezing  during  the  winter,  the 
vessels  containing  it  must  be  steam-heated. 

The  Glauber  salt  which  is  produced  when  H-acid  or  other  acid 
is  precipitated  must  be  recovered  as  it  has  a  considerable  value.  It 


SULPHONATIONS 


is  obtained  by  evaporating  down  the  mother-liquors,  and  is  frequently 
calcined  ;  it  may  be  used  directly  for  diluting  the  dyes  to  the 
commercial  strengths. 


Naphthylamine  Sulphonic  Acids  i :  6  and  1 :  7 

(Cleve's  Acids). 
Reaction  : 


SO,H 


NO2 
1\/\S03H        H03S< 


NH; 


NH, 


The  naphthylamine  sulphonic  acids  1:6  and  1:7  have  for  long 
been  of  great  technical  importance.  They  serve  for  the  manufacture 
of  important  black  cotton  colours  of  the  type  of  Columbia  Black  FF, 
and  also  for  the  production  of  a  whole  series  of  substances  of  the 
developed  colour  type  ;  for  instance,  the  important  Naphthogene 
Blue,  Zambesi  Black  V,  and  similar  products. 

Sulphonic  acids  again  of  this  type  are  also  frequently  made  use 
of  for  colours  such  as  Bayer's  Benzo  Fast  Blue  (q.v.). 

In  the  present  case  the  sulphonation  is  best  carried  out  according 
to  the  method  of  O.  N.  Witt  (in  passing,  it  may  be  noted  that  this 
process  has  long  been  in  practical  use  in  the  industry).  Contrary 
to  the  /?-naphthol  sulphonation,  an  excess  of  sulphuric  acid  is  used, 
but  this  does  not,  however,  represent  any  financial  loss,  as  a  further 
addition  of  sulphuric  acid  is  necessary  later  on,  as  we  shall  presently 
see.  Exactly  in  the  manner  described  on  p.  6,  206  gms.  of  92  %  2°6 
sulphuric  acid  (=66°  Be.)  are  run  into  128  gms.  best  quality  66°  Be4.' 

naphthalene  at  165°.     The  addition  should  occupy  at  least  half  an  I28  gms- 

.  ...  1        i  •   i    •        r  Naphthalene, 

hour,  as  otherwise  too  much  a-acid  is  produced,  which  is  of  no  use 

for  the  process.  The  mass  is  then  heated  for  a  further  half-hour  at 
165°,  in  order  to  convert  as  nearly  as  possible  the  whole  of  the 
a-acid  into  the  disulphonic  acid,  thus  obtaining  at  the  end  a  mixture 
of  1:6  and  1:7  nitro  acids  which  is  practically  free  from  isomeric 
a-acids.  It  is  then  cooled  down  to  60°  and  diluted  with  150  gms. 
sulphuric  acid  of  85  %.  (In  actual  practice  at  this  stage  the  mono- 
sulphonic  acid  is  blown  over  through  a  pipe  into  the  nitrating  vessel 


24  INTERMEDIATE  PRODUCTS 

by  means  of  compressed  air  ;  in  this  vessel  the  sulphuric  acid  required 
for  dilution  has  previously  been  placed.  Care  must  be  taken  not  to 
cool  too  much,  as  otherwise  under  certain  conditions  the  j3-sulphonic 
acid  may  solidify  in  the  pipes,  thus  leading  to  awkward  stoppages.) 
At  approximately  55°  the  mass  becomes  so  thick  that  it  is  almost 
impossible  to  stir  it ;  the  addition  is  now  begun  of  103  gms.  of 
60  %  nitric  acid  (=i  mol.=4O°  Be.).  The  mixture  rapidly  liquefies 
during  the  addition,  each  drop  acting,  so  to  speak,  as  a  lubricant. 
After  the  addition  of  the  first  few  grams  there  is  no  longer  any  danger 
of  solidification,  so  that  the  temperature  can  be  dropped  to  25°,  and, 
later  on,  even  to  10°  or  15°  (55°  is  far  too  high). 

In  the  laboratory  a  portion  of  the  naphthalene  sulphonic  acid 
always  separates  out  on  to  the  sides  of  the  vessel  and  the  stirrer. 
For  this  reason  it  is  absolutely  necessary  to  scrape  the  vessel  and 
the  stirrer  free  from  crust  with  a  sharp  iron  spatula  at  least  once 
during  the  operation,  as  soon  as  the  consistency  of  the  mass  permits 
of  this.  If  this  precaution  is  neglected,  it  may  easily  happen  that 
next  day  big  lumps  of  /^-naphthalene  sulphonic  acid  will  be  found 
floating  about  in  the  liquid.  On  the  large  scale  also  attention  must 
be  paid  to  this  point,  and  when  necessary  the  solid  portions  detached. 
Since  the  mass  behaves  differently  from  the  fluid  sulphonation 
mixture  of  the  1 13 :6-naphthalene  trisulphonic  acid,  as  we  have 
seen,  it  is  advisable  not  to  use  a  glass  stirrer,  but  one  made  of  cast-iron 
or  of  iron  rod  about  10  mm.  thick.  Acid  of  the  concentration  used 
has,  of  course,  practically  no  action  on  the  iron.  After  all  the  nitric 
acid  has  been  added,  which  will  take  about  2\  hours,  the  mixture 
is  allowed  to  stand  for  at  least  a  further  12  hours,  and  is  then  poured 
into  2  litres  of  water.  Practically  no  nitrous  fumes  are  evolved  in 
this  case. 

The  rest  of  the  process  may  now  be  continued  exactly  as  given 
for  the  reduction  of  nitro-naphthalene  trisulphonic  acid,  i.e.  liming, 
converting  into  the  sodium  salt  by  means  of  Glauber  salt,  reduction, 
and  evaporation.  This  process,  however,  is  not  quite  so  easy  in 
the  present  case,  as  the  sodium  salt  of  the  Cleve  acid  1:7  is  very 
difficultly  soluble,  and  consequently  often  separates  out  from  the 
dilute  reduction  liquor.  For  this  reason  it  is  better  in  the  present 
case  to  reduce  the  unchanged  calcium  salt,  and  then,  after  concentra- 
tion, to  precipitate  the  amino  acids  with  hydrochloric  acid. 

Still  neater,  however,  is  a  process  which  has  long  been  in  use 
by  Bayer  &  Co.  Instead  of  reducing  the  lime  or  sodium  salt  the 
magnesium  salt  is  employed.  For  this  purpose  sufficient  magnesite 
to  combine  with  all  the  sulphonic  acid  is  added  before  the  addition 


PLATE   III, 


FIG;  8. — Hydraulic  press  and  pump  with  automatic  cut-out  (made  by  Bucher- 
Mauz,  Niederweningen,  Canton  Zurich),  i.  Cast-steel  cylinder.  2.  Platform. 
3.  Pipe  for  compression  water  (250  atms.).  4.  Pump  with  automatic  cut-out 
at  250  atms.  (The  pressure  may  be  varied  by  moving  the  weight ;  one 
pump  can  serve  4-6  presses  easily.)  5.  Cast-steel  head-piece. 


SULPHONATIONS  25 

of  the  lime  or  chalk  ;    in   the   present  case  45  gms.  MgCO3  will  45  gms. 
suffice.     The  liming  out  is  then  performed  exactly  as  given  on  ^o^t°3 
p.  15.     There  are  no  further  difficulties  in  the  reduction,  but  great  320  gms. 
care  must  be  taken  that  the  best  iron  be  used  as  the  reduction  of  CaCOa- 
Cleve's  acid  readily  stops  at  the  hydroxylamine  stage  ;    either  sul- 
phuric acid  or,  better,  acetic  acid  may  be  used  for  the  reduction, 
which  is  carried  out  as  described  on  p.  16.     As  soon  as  the  reduc- 
tion liquid   has   become   quite   colourless,   sufficient  magnesite   or 
calcined  magnesia  is  added  to  give  a  slight  but  distinct  alkaline 
reaction  to  litmus.     Since  both  magnesia  and  magnesite  are  very 
sparingly  soluble  a  pronounced  blue  reaction  cannot  be  given  with 
the  test  paper.     The  product  is  then  filtered,  the  iron  oxide  well 
washed,  and  the  liquid  evaporated  down  in  a  basin  to  i  litre.     The 
sodium  salt  of  the   i  ly-naphthylamine  sulphonic  acid  is  sparingly 
soluble,  that  of  the  1:6,  however,  easily  so. 

A  strong  solution  of  common  salt  is  now  added  until  the  total 
concentration  in  the  liquid  is  about  6  %.  About  300  c.c.  will  be 
required.  The  sodium  salt  of  the  i:y-acid  is  completely  precipi- 
tated during  the  course  of  a  day.  The  precipitate  is  filtered  off 
and,  after  acidifying  the  mother-liquor  with  concentrated  sulphuric 
or  hydrochloric  acid,  the  free  i  :6-naphthylamine  sulphonic  acid  is 
precipitated  after  standing  several  days.  Both  acids,  the  1:7  as 
well  as  the  1:6,  are  somewhat  impure  because  isomeric  products 
are  always  formed  in  addition  to  the  desired  acids. 

Modifications. — If  it  is  desired  to  obtain  quite  pure  Cleve  acids, 
which  will  usually  be  the  case,  the  process  must  be  carried  out  some- 
what differently.  Instead  of  separating  the  1:7  acid  from  the 
reduction  liquor  after  evaporation  by  salting  out  with  common  salt, 
the  whole  may  be  made  distinctly  mineral-acid  by  means  of  sulphuric 
or  hydrochloric  acid  ;  in  the  course  of  two  or  three  days  a  thick 
precipitate  of  a  mixture  of  the  1:6-  and  1 7-naphthylamine  sul- 
phonic acids  will  be  formed,  which  is  thoroughly  washed  on  a  suction 
filter  with  cold  water.  The  mother-liquor  is  coloured  violet  and 
always  contains  hydroxylamines.  It  will  use  up  to  20  gms.  sodium 
nitrite  on  diazotization,  corresponding  to  about  28  %  of  theory  of 
the  sulphonic  acid.  With  careful  working,  however,  and  especially 
by  paying  special  attention  to  the  reduction,  the  losses  may  be 
diminished  to  less  than  20  %.  After  protracted  washing  on  the 
filter  the  acids  become  quite  pale  in  colour.  A  small  portion  of 
the  sulphonic  acids  is  lost  by  so  doing,  but  a  particularly  pure 
substance  is  obtained  in  this  manner. 

The  Cleve  acids,  washed  free  from  impurities,  isomers,  and 


26  INTERMEDIATE  PRODUCTS 

1 1.  water.        disulphonic  acids,  are  now  dissolved  in  i  litre  of  water  and  about 

NaaOOJ.          35  gms-  soda.     50  Gms.  of  finely  powdered  common  salt  are  then 

50  gms.  added  quickly  to  the  hot  soda  solution  of  the  mixture,  which  is  then 

allowed  to  stand  for  one  day  with  continuous  mechanical  stirring. 

The  Cleve  acid    1:7  separates  out  in  an  extremely    pure  form  as 

the  sodium  salt,  which  is  filtered  off  and  washed  with  a  very  little 

ice-cold  water,  after  which  it  is  pressed. 

The  mother-liquor  from  the  1:7  acid  is  acidified  as  described 
above,  and  gives  a  good  1:6  acid.  For  complicated  azo-colours, 
such  as  Columbia  Black  FF,  Zambesi  Black  V,  and  so  forth,  it  is, 
however,  advisable  to  purify  this  product  once  more  by  solution 
and  reprecipitation.  The  purer  the  intermediate,  the  greater  the 
yield  of  finished  colour. 

Yield :        Cleve  acid  1:7      .          -7°  gms-  (M.W.  223). 
„       „     1:6    V       .     80  gms. 

Notes  on  Works  Technique  and  Practice. — The  same  considera- 
tions hold  good  for  the  sulphonation  of  naphthalene  in  quantities 
of  200-300  kgs.  and  over  as  were  noted  in  discussing  H-acid. 
Here,  also,  the  sulphonation  takes  much  longer  than  in  the  laboratory, 
corresponding  to  the  larger  quantities  used.  Again,  the  reduction 
must  be  watched  very  carefully,  as  the  Cleve  nitro-sulphonic  acids 
are  much  harder  to  reduce  than  the  naphthalene  nitro-polysulphonic 
acids.  The  partially  reduced  acids  are  hydroxylamine  sulphonic 
acids,  which  appear  finally  in  the  mother-liquors  and  render  the 
Cleve  1:6  acid  in  particular  very  impure  ;  but  if  the  reduction  is 
carried  out  very  exactly  the  crude  1:6  acid  will  be  fairly  pure. 
On  the  large  scale  the  mother-liquors  are  always  evaporated  down 
separately,  and  a  second  crop  of  crystals  obtained  which  require 
about  10  parts  of  nitrite  per  molecule,  corresponding  to  about 
30  kgs.  impure  sulphonic  acids. 

The  red  coloration  which  nearly  always  appears  on  leaving 
impure  Cleve  acids  exposed  to  the  air  in  the  presence  of  moisture, 
is  caused  exclusively  by  the  oxidation  of  the  hydroxylamine  acids. 
Pure  Cleve  acids  are  stable  in  air  and  give  almost  identical  azo  dyes. 
The  observation  is  often  made  that  the  1:7  acid  affords  better 
yields  of  colouring  matters.  This  is  quite  correct,  but  does  not 
depend,  however,  on  the  1:7  acid  as  such,  but  upon  the  fact  that 
this  acid  is  separated  as  its  sodium  salt,  and  is  therefore  much  purer 
than  the  1:6  isomer  which  is  obtained  as  the  free  acid.  According 
to  my  own  experience,  a  pure  1:6  acid  yields  dyes  identical  in 
strength  and  shade  with  those  from  the  1:7  acid.  The  differences 


SULPHONATIONS  27 

in  shade  which  are  frequently  observed  are  so  insignificant  that  they 
come  within  the  limits  of  technical  errors. 


Naphthylamine  Sulphonic  Acids  1:5  and  i  :8. 

Reaction  : 

N02  S03H        NH2  S03H 


SO,H 


The  preparation  of  the  naphthylamine  sulphonic  acids  1:5  and 
1:8  is  closely  connected  with  that  of  the  Cleve  acids.  They  are 
amongst  some  of  the  most  widely  used  intermediates. 

In  order  to  obtain  the  a-sulphonic  acid,  it  is  preferable  to  carry 
out  the  sulphonation  at  a  temperature  below  the  melting-point  of 
naphthalene  (below  80°).  128  Gms.  of  very  finely  divided  naphtha-  I28 
lene  l  are  rapidly  added  to  260  gms.  of  sulphuric  acid  (mono- 
hydrate)  at  o°.  The  sulphonation  begins  at  once,  and  if  the  mixture  H2SO4 
be  left  to  itself  after  the  addition  it  will  solidify  suddenly  to  a  cement- 
like  mass  as  soon  as  the  first  crystals  of  the  naphthalene  sulphonic 
acid  begin  to  separate.  The  laboratory  stirrer  is  incapable  of  dealing 
with  this  hard  mixture  and  will  stop  ;  it  is  therefore  a  good  plan 
to  inoculate  with  a  small  quantity  of  solid  a- acid  as  soon  as  the 
naphthalene  has  been  added.  The  material  for  this  inoculation 
may  be  prepared  by  warming  a  small  portion  of  naphthalene  with 
sulphuric  acid  on  the  water-bath  and  then  cooling  the  mixture. 
This  inoculation  causes  the  sulphonic  acid  formed  to  separate  out  at 
once,  and  prevents  it  from  crystallizing  out  from  the  super-saturated 
solution.  The  sulphonation  mixture,  therefore,  thickens  slowly, 
and  a  sudden  solidification  is  no  longer  to  be  feared. 

The  temperature  rarely  rises  above  35°,  for  which  reason  it  is 
necessary  to  use  pure  monohydrate,  or  else  part  of  the  naphthalene 
will  remain  unattacked.  In  any  case,  however,  it  will  be  found 
that  a  small  portion  escapes  sulphonation  on  occasions.  When  this 

1  96  %  of  the  ground  substance  should  pass  through  a  sieve  having  400  meshes 
to  the  square  cm. 


28  INTERMEDIATE   PRODUCTS 

occurs  the  mass  should  be  heated  to  60°  on  the  water-bath  and 
stirred  until  all  the  naphthalene  has  disappeared.  It  is,  however, 
by  no  means  easy  to  carry  out  the  sulphonation  smoothly  on  a  small 
scale,  and  a  fair  amount  of  practice  is  required  for  such  operations. 
In  order  to  ascertain  how  much  naphthalene  there  is  in  the  sulpho- 
nation mixture  a  small  portion  should  be  dissolved  in  water,  when  the 
unattacked  naphthalene  separates  out  on  the  bottom  of  the  test-tube. 
On  the  large  scale  no  difficulty  is  found  in  carrying  out  this 
sulphonation. 

103  gms.  The  nitration  is  carried  out  exactly  as  for  the  preparation  of 

HN(V  Cleve  acid,  except  that  it  is,  in  this  case,  unnecessary  to  add  a  second 

40°  °B6.  quantity  of  sulphuric  acid  as  the  whole  amount  is  added  at  the 

45  gms.  start.     The  reduction  and  separation  of  the  two  isomeric  naphthyl- 

MgCO3  amine  sulphonic  acids  is  also  effected  as  described  for  Cleve  acid, 

about  320 

gms.  CaCO3.  The  sodium  salt  of  the  1:8  acid  is  even  more  insoluble  than  that 
300  gms.  Fe.  o£   the  I:J-  acid    so  that  the  separation  is  still  easier  in  this  case. 

20  c.cs. 

Acetic  acid      A    i:8  acid  is  obtained  which  is  practically  free  from  Cleve  acids, 
(40  %)•  with  the  exception  of  very  small  quantities  which  are  always  formed 

in  spite  of  the  low  temperature  of  sulphonation. 

The  yield  of  1:8  add  is  about  100  gms.  of  100  %  product 
(M.W.  223)  ;  whilst  that  of  the  1:5  acid,  which  is  obtained  by 
precipitating  with  sulphuric  acid,  amounts  to  40  gms.  of  100  %  product 
(M.W.  223). 

Modifications    of    the   Process. — The    naphthylamine    sulphonic 

acids    1:5    and    1:8  are  distinguished  from  other  acids   by  the  fact 

that  they  can  also  be  isolated  in  the  presence  of  considerable  quantities 

of  iron  salts.     Instead  of  liming  out  and  then  reducing  the  magnesium 

salt,  the  nitro  acids  may  be  diluted  with  water,  and  then  allowed  to 

260  gms.  Fe.  run  on  to  iron  turnings,  with  vigorous  stirring.     Care  must  be 

taken,  however,  that  the  solution  remains  neutral  to  Congo  ;    it 

heats  up  to  80°,  but  no  sulphonic  acid  separates  out.     Only  after 

heating  the  finished  reduction  mass  for  some  time  to  boiling  does 

40  gms.  Fe.     the  violet  coloration  gradually  give  place  to  a  greenish  one.    40  Gms. 

of  iron  powder  are  added  cautiously,  whilst  the  liquid  is  heated  at 

the  boiling-point  until   the  ferrous  salts  of  the  1:5  and  1:8  acids 

separate   out   as   greyish- white   crystals.     After   cooling   these   are 

About  60        decomposed  by  means  of  sulphuric  acid  until  the  liquid  is  distinctly 

H^SQ0110        mineral  acid.     The  free  sulphonic  acids  are  filtered  off,  the  ferrous 

sulphate  is  well  washed  out,  and  the  residue  dissolved  with  the  aid 

40  gms.  of  40  gms.  of  magnesite.     The  filtered  magnesium  salts  on  salting 

Magnesite.      Qut  ^^  IQ  o^  of  COmmon  salt  (calculated  on  the  amount  of  liquid) 

yield    an  extraordinarily  pure    1:8  acid,  which  is  completely  free 


SULPHONATIONS  29 

from  Cleve  acid.  The  filtrate  from  the  sodium  salt  of  the  1:8  acid 
gives,  on  acidifying,  an  extremely  pure  1:5  acid,  as  the  Cleve  acids 
are  only  reduced  to  the  hydroxylamine  stage,  and  are  washed  away 
with  the  iron  sulphate. 

Notes  on  Works  Technique  and  Practice. — On  the  works  scale 
the  sulphonation  of  the  finely  powdered  naphthalene  must  be 
carried  out  in  a  manner  somewhat  different  from  the  laboratory 
methods.  First  of  all,  it  is  necessary  to  make  use  of  freshly-ground 
naphthalene,  as  it  rapidly  cakes  together.  The  best  way  is  to  run 
the  mass  through  the  disintegrator  on  the  previous  evening,  and 
then  to  run  it  through  once  more,  or  twice  more  if  necessary, 
immediately  before  the  sulphonation  ;  it  must  then  be  added  to 
the  sulphuric  acid  as  rapidly  as  possible.  For  this  purpose  it  is 
very  convenient  to  heap  up  the  naphthalene  in  an  open  box  from 
which  it  may  be  transferred  to  the  vessel  by  a  wooden  shovel.  To 
ensure  that  no  lumps  of  the  snow-like  substance  get  into  the  acid  a 
coarse  sieve  provided  with  a  funnel  should  be  placed  over  the  opening 
into  the  vessel.  As  soon  as  all  the  naphthalene  has  been  added  the 
mass  is  "  seeded  "  and  the  sulphuric  acid  and  naphthalene  mixed 
at  once  by  means  of  an  iron  stirrer  of  the  anchor  type,  as  shown  in 
Plate  II.  In  spite  of  careful  cooling  the  temperature  of  the  porridge- 
like  mass  rises  slowly  to  18°,  and  then  suddenly,  owing  to  the  heat 
of  crystallization,  it  rises  to  about  58°.  For  this  reason  the  action 
of  the  sulphuric  acid  is  considerably  more  energetic  in  this  case 
than  in  the  laboratory,  so  that  it  is  necessary  to  dilute  the  mono- 
hydrate  with  3  kgs.  ice  to  about  98  %.  The  naphthalene  dis- 
appears completely  in  the  course  of  ij  hours  if  it  has  been  finely 
enough  powdered.  The  reduction  is  carried  out  as  given  under 
H-acid,  as  also  is  the  evaporation  of  the  reduction  liquor. 

If  the  modified  process  be  used  iron  reduction  vessels  cannot, 
of  course,  be  utilized,  and  it  is  found  to  be  most  convenient  to  adopt 
wooden  tubs,  which  last  a  long  time. 

The  filtration  of  the  free  sulphonic  acids,  which  have  been 
precipitated  by  means  of  sulphuric  acid,  is  effected  by  means  of 
filter-presses  using  felt  filters.  The  better  the  product  has  been 
washed  out,  the  easier  is  the  extraction  by  means  of  magnesia.  It 
is  advisable,  however,  to  boil  out  the  residue  with  water  once  or 
twice  more,  as  otherwise  considerable  quantities  of  the  acid  may  be 
lost  in  the  magnesia-iron  sludge. 

On  the  large  scale  it  is  not  usual  to  precipitate  the  j:8  acid  as 
the  sodium  salt  by  simply  sprinkling  in  common  salt,  but  instead  a 
solution  of  salt  is  allowed  to  run  in  during  an  hour  (otherwise  some 


3° 


INTERMEDIATE  PRODUCTS 


1:5  acid  will  be  carried  down  with  it).  Both  methods  appear, 
however,  to  be  of  about  the  same  value. 

The  i  :8-naphthylamine  sulphonic  acid  or  peri-acid  is  not  used 
directly  as  such  for  the  preparation  of  dyes,  but  is  first  converted 
into  various  other  compounds.  The  most  important  of  these  are 
Naphtha-sultone,  Phenyl-naphthylamine  sulphonic  acid  1:8  (Phenyl- 
peri-acid),  and  the  Amino-naphthol  sulphonic  acids  1:8:4  an<^  1-8:2:4. 

Their  method  of  formation  is  shown  in  the  following  scheme  : — 


S03  N2 


SO,  O 


I. 


Naphtha-sultone. 


HO 


NH 


H0S 


Peri-acid. 


Phenyl-naphthylamine  sulphonic  acid  1:8. 


H03S      NH 


III. 


IV. 


S03H 

I 
OH  NH2 

^^SOJI 


S03H 

S-acid,  or  amino-naphthol 
sulphonic  acid  1:8:4. 


S03H 

Amino-naphtholdisulphonic 

acid  1:8:2:4. 
Chicago-acid,  or  SS-acid. 


The  naphthylamine  sulphonic  acid  1:8  may  be  converted  into 
the  diazo  compound  on  treatment  with  nitrous  acid  (sodium  nitrite) 
in  mineral  acid,  solution  at  25°.  On  heating  this  in  aqueous  solution 
to  55°  a  quantitative  yield  is  obtained  of  naphtha-sultone  (I.).  The 
yield  of  sultone  obtained  is  a  direct  measure  of  the  purity  of  the 
starting  material  ;  it  is  practically  always  converted  into  the  naphtha- 
sultone  sulphonic  acid  which,  on  coupling  with  azo  components, 


SULPHONATIONS  31 

yields  dyes  which  are  very  pure  and  fast  to  light.  During  recent 
years,  however,  the  importance  of  these  colouring  matters  has 
diminished  considerably. 

Again,  the  naphthylamine  sulphonic  acid  1:8  may  be  con- 
verted into  its  arylated  derivatives  ;  thus  the  technically  important 
phenyl-naphthylamine  sulphonic  acid  1:8  may  be  obtained  by 
heating  the  free  naphthylamine  sulphonic  acid  with  aniline  (II.). 

One  part  of  the  free  sulphonic  acid  is  heated  with  three  times  its 
weight  of  aniline  (or  />-toluidine)  to  160°  in  an  enamelled  vessel, 
which  is  heated  in  an  oil  bath.  The  water,  which  is  always  present  in 
the  substance,  is  distilled  off  in  vacuum,  the  product  being  afterwards 
heated  for  24  hours  with  continuous  stirring.  The  excess  of  aniline 
is  carefully  distilled  off,  the  aniline  salt  of  the  resultant  phenylated 
acid  is  then  decomposed  by  means  of  the  calculated  quantity  of 
soda-lye,  and  the  residual  aniline  is  driven  off  with  steam,  thus 
obtaining  a  solution  of  the  phenyl-naphthylamine  sulphonic  acid, 
which  is  then  coupled  directly  with  diazotized  H-acid  in  acetic  acid 
solution.  If  the  process  has  been  correctly  carried  out,  the  acid 
itself  need  not  be  isolated.  The  resultant  dye  is  Sulphon  Acid  Blue  R 
(Bayer),  which  is  fast  to  light. 

If  the  naphthylamine  sulphonic  acid  is  sulphonated  with  oleum, 
the  di-  or  tri-sulphonic  acid  is  produced  (or  the  anhydro  compounds, 
the  Naphthasultams)  according  to  the  strength.  These  two  products 
are  fused  vwith  caustic  potash  in  an  open  pan  at  200-210°,  and  yield 
the  corresponding  amino-naphthol  sulphonic  acids  (III.  and  IV.). 
Both  are  intermediates  for  the  production  of  wool  and  cotton  colours. 

Naphthylamine  sulphonic  acid  1:5  is  of  less  importance,  and  can 
only  be  dealt  with  briefly.  It  is  either  diazotized  and  coupled  with 
amines  and  naphthols,  or  is  worked  up  into  amino-naphthol  sulphonic 
acid  1:5:7. 

NH2  NH.COCH3      NHCOCH3  NH2 

HO3S|7  I     .   HO3S|? 


£ 

S03H  S03H  S03H 

As  indicated  in  the  above  scheme,  the  1:5  acid  differs  from  the 
1:8  acid,  in  that  it  must  be  acetylated  before  sulphonation,  as  it  is 
otherwise  destroyed  by  the  sulphuric  anhydride.  Acetylations  of 
this  kind  play  a  not  unimportant  part  in  the  technology  of  dyes 
(cf.  Amidonaphthol  Red  G). 


32  INTERMEDIATE  PRODUCTS 

Sulphonation  of  /2-Naphthol 

On  sulphonating  /2-naphthol  a  considerable  number  of  mono- 
and  poly-sulphonic  acids  are  obtained  according  to  the  concentration 
and  the  temperature  of  the  sulphuric  acid  used.  Only  a  few  typical 
cases  will  be  discussed,  in  order  that  the  beginner  may  be  able  to 
arrive  at  an  idea  of  this  branch  of  manufacture  of  intermediate 
products. 

As  is  well  known,  /3-naphthol  sulphonates  chiefly  in  the   6- 
position  on  treatment  with  sulphuric  acid  of  66°  Be.  (93  %)  ;   that 
is    to    say,  naphthol  sulphonic  acid  2:1  is  first  formed, .  which  is 
rapidly  isomerized  to  the  2:6  acid  (SchafFer  acid). 
Reaction  : 

S03H 
r  /\    , 
iOH 


KY>1 

L\/\/ 


Schaffer  acid. 

If  an  excess  of  acid  be  used,  a  certain  amount  of  the  2:3:6  and 
2:6:8  acids  are  always  formed  as  well  which,  owing  to  their 
property  of  combining  with  diazonium  compounds  to  give  respectively 
reddish  or  yellowish  dyes,  are  usually  known  by  the  names  of  R-acid 
and  G-acid.1 
Formulas  : 

HO3S 
$ 

SO3H  HO3S6 


R-acid.  G-acid. 

According  to  whether  the  sulphonation  is  warm  or  cold,  relatively 
more  R-  or  G-acid  is  formed  respectively.  All  three  of  the  acids 
in  question  are  important  intermediates  for  the  production  of  azo 
colours.  As  it  is  absolutely  impossible  to  obtain  the  three  isomers 
by  themselves,  it  becomes  necessary  to  separate  them  very  carefully 
from  their  mixture. 

•It  is  important  to  emphasize  the  fact  that  the  j3-naphthol  which  is 
to  be  used  must  be  powdered.  If  this  elementary  precaution  be 
neglected,  that  portion  of  the  naphthol  which  first  enters  into  reaction 
becomes  sulphonated  at  the  expense  of  the  coarse  lumps,  which  swim 
about  in  the  reaction  mass,  and  it  is  impossible  to  obtain  uniform 
results.  This  will  also  be  the  case  if  the  reaction  mixture  be  allowed 
1  German  :  Rot  =  red  ;  Gelb  =  yellow. 


SULPHONATIONS  33 

to  stand  instead  of  being  continuously  stirred.     The  apparatus  is 
the  same  as  that  for  /2-naphthalene  sulphonic  acid. 

Naphthol  Sulphonic  Acid  2:6  and  Disulphonic  Acid  2:3:6 
(Schaffer  Acid  and  R-acid). 

142   Gms.  (i   mol.)  of  pure,  finely  powdered  /2-naphthol  are  200  gms. 
added    to  200  gms.  of    100  %  sulphuric  acid  with  stirring.     The  ^f  S4' 
temperature  rises  rapidly  to  about  80°,  at  which  it  is  left  for  about   142  gms. 
a  quarter  of  an  hour  to  ensure  a  homogeneous  mixture.     The  tern-   P-naPhtho1- 
perature   is  then  raised  to  100-110°,  stirring  continuously,  until  a 
test  portion  no  longer  shows  any  separation  of  /3-naphthol  on  pouring 
into  water.     This  will  occupy  about  3  hours.     The  mixture  is  then 
poured  into  i  litre  of  water,  and  is  neutralized  with  about  200  gms.  200  gms. 
calcium  carbonate.     A  warm  solution  of  Glauber  salt  is  now  added  CaC°3- 
to  the  pasty  gypsum  mixture.     A  clear,  filtered  test  portion  should 
not  give  any  turbidity  with  Glauber  salt.     The  whole  is  then  filtered 
and  the  gypsum  washed  out.     (For  this  purpose  the  factories  make 
use  of  waste  Glauber  salt  from  the  H-acid  or  other  caustic  soda  melt, 
which  they  can  obtain  at  less  than  i   franc  per  100  kgs.)      The 
sodium  salts  are  evaporated  down  in  a  porcelain  dish  over  a  bare 
flame  to  half  a  litre  (a  vacuum  is  used  in  the  works)  and  the  relatively 
sparingly  soluble   sodium-2:6-sulphonate   salted  out  with  sufficient 
common  salt  for  the  solution  to  contain  20  %  of  salt  (in  the  present 
case    100    gms.).     With  good  stirring  the  Schaffer  salt  separates  100  gms. 
out  completely  during  the  course  of  a  day.     It  is  filtered  off  and  Salt< 
washed  with  a  very  little  concentrated  brine.     The  aqueous  solution 
of  the  Schaffer  salt  purified  in  this  manner  should  show  only  slight 
fluorescence.     The  filter  cakes  are  well  pressed  in  a  screw-press  and 
consist  of  very  pure  Schaffer  salt,  containing  only  a  very  little  R-salt. 
The  mother-liquor  is  acidified  with  concentrated  sulphuric  acid  and 
allowed  to  stand  for  some  time.     In  the  laboratory,  10-12  hours 
will  suffice,  but  on  the  large  scale  several  days  are  required,  before 
the  acid  sodium  salt  of  R-acid  has  separated  out  completely.     It  is 
extremely  easily  soluble,  so  that  in  some  circumstances  the  mother- 
liquor  itself  can  be  coupled  directly  with  an  azo  component  to  a  dye 
of  the  Ponceau  series  (e.g.  with  meta-xylidine  to  give  Ponceau  R). 

If  it  is  desired  to  obtain  more  R-acid  than  Schaffer  acid  the 
quantity  of  sulphuric  acid  is  increased,  so  that  finally  2:3:6- 
naphthol-disulphonic  acid  is  obtained  almost  exclusively. 

Yield : 

1 60  gms.  Schaffer  salt  (100  %)  approximately. 
80  gms.  R-salt  (100  %)  approximately. 

3 


34  INTERMEDIATE  PRODUCTS 

The  method  for  the  determination  of  R-salt  and  Schaffer-salt  is 
given  in  detail  in  the  analytical  portion. 

2:3:6-  and  2:6:8-Naphthol-disulphonic  Acid  (R-salt  and  G-sali). 

G-salt  has  long  been  a  much  more  important  product  than  R-salt 
owing  to  the  fact  that  the  former  acid  is  the  starting-point  for  amino- 
naphthol-sulphonic  acid  2:8:6  (Gamma- acid),  which  is  used  in 
increasing  quantities  for  the  production  of  a  large  number  of  wool 
and  cotton  dyes.  The  preparation  of  this  substance  is  by  no  means 
simple,  for  which  reason  the  various  German  works  which  manu- 
facture y-acid  have  signed  a  convention  which  binds  them  not  to 
sell  it  to  outsiders  below  a  certain  price,  which  before  the  war  was 
about  four  francs  per  kilo. 

The  naphthol-sulphonic'1  acid  2:6:8  can  be  readily  converted 
into  the  corresponding  amino-naphthalene  sulphonic  acid,  thus 
obtaining  amido-G-acid,  which  affords  a  good  yield  of  y-acid  when 
fused  with  caustic  soda.  Instead  of  starting  from  the  naphthol- 
disulphonic  acid,  the  naphthylamine  sulphonic  acid  may  equally 
well  be  used,  which  is  obtained  by  the  direct  sulphonation  of 
j3-naphthylamine.  The  diagram  on  p.  36  illustrates  these  various 
relationships  more  clearly  than  any  description.  On  the  same 
page  full  details  as  to  the  preparation  of  the  isomeric 
j8-naphthylamine  sulphonic  acids^  are  given,  and  of  their  fusion 
with  alkalis. 

Since  more  G-acid  than  R-acid  is  obtained  at  lower  temperatures, 

it  is  necessary,  in  order  to  obtain  the  former  acid,  that  a  temperature. 

142  gms.         of  30-35°  should  not  be  exceeded,  which  necessitates  the  use  of  a 

£~]Japhgho1'     somewhat  larger  excess  of  sulphuric  acid.     Again  it  is  necessary 

H2SO4,  to  powder  the  naphthol  finely  ;  it  is  then  added  slowly  to  three  times 

ioo  %.  jts  wejght  of  sulphuric  acid  (monohydrate),  the  temperature  being 

kept  as  low  as  possible  by  careful  cooling.     It  must  be  remembered, 

however,  that  whilst  the  thermometer  may  show  for  example  20°, 

overheating  may  nevertheless  occur  where  the  j8-naphthol  drops  into 

the  acid.    This  is  particularly  the  case  on  the  large  scale,  where,  for 

instance,  at  least   5    hours   must  ^be   allowed  for  the   addition   of 

288  kgs.  naphthol.     Cooling  by  means  of  circulating  brine  is  by 

far  the  best  method. 

The   sulphonation,  in  distinction   from   that   for   R-acid,  does 

not  occupy  merely  a  few  hours,  but  frequently  takes  2—4  days. 

Stirring  must  be  continued  until  a  test  portion  diluted  with  a  very 

.  little  water  no  longer  gives  any  precipitate.     If  this  is  not  the  case 


8ULPHONATIONS  35 

within  two  days  it  is  best  to  add  a  little  more  moiiohydrate  of,  very 
cautiously,  a  very  little  fuming  sulphuric  acid  containing  not  more 
than  15  %  SO3.  The  sulphonation  is  then  finished  after  a  further 
2-3  hours. 

The  sulphonated  product  is  poured  into  a  litre  of  water  and  i  1.  water. 
treated  with  lime  or  chalk  as  given  under  R-acid.     The  calcium  salt 
is  not  decomposed  by  means  of  a  sodium  salt,  but  either  potassium 
carbonate  is  added  to  its  solution  until  all  the  lime  has  been  pre- 
cipitated as  chalk,  or  more  cheaply  commercial  90  %  potassium  ca.  150  gm 
sulphate  is  employed.     The  filtered  solution  of  the  potassium  salt  3 


so  obtained  is,  in  the  laboratory,  evaporated  down  over  a  bare  flame 

to  400  c.c.  (for  i  gram-mol.).     Sufficient  hydrochloric  acid  is  added  About  100 

to  render  the  product  strongly  mineral  acid,  about  100  grams  being  gms> 

required.     On  cooling,  the  acid  potassium  salt  of  the  naphthol- 

sulphonic    acid    2:6:8  separates    out    in    a  completely  pure    form, 

and  after  standing  for  a  day  (or  1-2  days  on  the  large  scale),  it  is 

filtered  off,  washed  with  a  little  10  %  potassium  chloride  solution, 

and  well  pressed.     Centrifuging  is  the  best  means  for  extracting  as 

much  mother-liquor  as  possible.     The  mother-liquor  containing  all 

the  R-salt  is  either  salted  out  with  150  gms.  common  salt,  or  may  be 

worked  up  directly  into  colour. 

Yield  from  142  gms.  j8-naphthol  : 

about  160  gms.  G-salt  (acid  potass,  salt,  M.W,  341) 
about  145  gms.  R-salt  (M.W.  341). 


Amino-naphthol    Sulphonic   Acids   2:6:8   and   2:5:7 
(y-acid  and  J-acid),  from  /3-naphthylamine. 

y-acid  is  always  prepared  from  /3-naphthol  by  one  of  two  methods. 
Either  the  so-called  G-salt  (cf.  p.  32)  is  converted  into  amido-G-salt 
by  heating  with  20  %  ammonia  to  240°, 1  the  latter  being  then  melted 
to  y-acid  ;  or  the  ^-naphthol  is  first  converted  into  /3-naphthylamine 
(q.v.),  which  on  disulphonation  gives  amido-G-acid  and  other 
isomers.  The  method  for  the  separation  of  these  acids  is  described 
in  detail  in  the  next  few  pages,  as  also  the  melt  of  the  pure  amino- 
disulphonic  acids.  The  diagram  on  the  next  page  will  explain  the, 
above  statements, 

1  Caution  .   Pressure  about  50  atmos. 


36  INTERMEDIATE  PRODUCTS 

p-Naphthylamine  Disulphonic  Acids. — On  sulphonating  jS-naph- 
thylamine  at  least  three  isomers  are  always  produced,  as  may  be 
seen  from  the  following  scheme.  The  separation  is  by  no  means  easy, 
and  can  only  be  carried  out  in  the  laboratory  by  maintaining  certain 
very  exact  conditions.  On  the  works  scale  it  is  easier  to  carry  out 
as,  owing  to  the  larger  quantities  dealt  with,  the  fractional  crystalliza- 
tion can  be  more  readily  supervized. 


Reactions  : 


2|OH 

H°3S\A/S03H 

fc  R-acid. 

t 


OH 


OH 


NH 


NH< 


H08SI« 


Amino-naphthol  sulphonic 
acid  2:6:8.     (y-acid.) 


fi-naphthyl- 
amine. 


H03S 


OH 

Amino  -naphthol  sulphonic 

acid  2:5:7. 
(Iso-y-acid,  J-acid.) 


S0H 


We  start  with  the  completely  dry  j8-naphthylamine  sulphate  as 
obtained  by  precipitation  from  the  hydrochloride  in  the  preparation 
of  jS-naphthylamine  (q*v.).  The  quantitative  estimation  of  the 
sparingly  soluble  sulphate  is  carried  out  by  dissolving  a  weighed 
portion  in  concentrated  sulphuric  acid  at  60°,  pouring  the  clear 
solution  into  water,  and  adding  i  c.c.  of  hydrochloric  acid.  Without 
the  addition  of  hydrochloric  acid  it  is  practically  impossible  to 


SULPHONATIONS  37 

diazotize  the  substance.     j8-naphthylamine  sulphate  which  has  been 
properly  made  should  be  about  97  %  pure. 

192  Cms.  of   the    sulphate   (=i  gm.-mol.)  is  ground    up  very   192  Naph- 
fine,  well  rubbed  up  with  i  gm.  of  calcined  soda,  and  then  added  j^JJ™ * 
to  560  gms.  of  sulphuric   acid   monohydrate  at  a  temperature  of  560  gms. 
30-60°.     It  is  then  heated  at  65°  until  a  test  portion  gives  a  clear  J^f  %4' 
solution  with  soda  ;  this  should  take  about  an  hour,  the  whole  time 
occupied  from  the  first  addition  to  complete  sulphonation  being 
about  3  hours. 

A  process  suggested  for  obtaining  the  2:5  acid  in  a  pure  con- 
dition as  the  sodium  salt  consists  in  liming,  treating  with  soda, 
evaporation,  and  extraction  of  the  dry  salts  with  95  %  alcohol.1 
This  method  is  actually  carried  out,  and  is  strongly  to  be  recom- 
mended if  it  is  simply  a  question  of  obtaining  the  2:5  acid  in  a 
pure  condition.  If,  however,  the  disulphonic  acids  are  to  be 
prepared  this  expensive  separation  is  unnecessary,  and  the  crude 
product  is  simply  sulphonated  straight  away. 

The  mixture  of  the  isomeric  monosulphonic  acids  is  cooled 
down  to  40°  with  continuous  stirring,  and  is  then  treated  cautiously 
with  500  gms.  of  oleum  (66  %  SO3)  during  2  hours,  the  tempera-  soo  g^ 
ture  not  being  allowed  to  exceed  55°.  The  sulphonation  is  con-  Oleum ; 
tinued  until  a  test  portion  dissolves  readily  and  completely  in  a 
little  ice-water  without  any  subsequent  turbidity  ;  this  is  absolutely 
necessary  if  the  later  separation  of  the  mixture  is  to  be  successful. 
When  the  sulphonation  has  gone  thus  far,  it  must  not  be  stopped, 
but  must  then  be  allowed  to  continue  at  55-65°  for  several  hours, 
as  it  has  been  found  that  only  in  this  way  can  success  be  assured  ; 
only  when  the  mixture  has  been  thoroughly  sulphonated  does  the 
separation  succeed.  Too  strong  an  oleum  must  not  be  used,  as 
otherwise  too  much  substance  is  destroyed,  and  the  temperature 
of  the  sulphonation  must  not  exceed  65°.  This  operation  will  last 
about  2  days,  and  must  not  be  hurried.  The  sulphonated  mixture, 
which  still  contains  a  little  free  SO3,  is  poured  in  a  thin  stream  into 
a  mixture  of  950  c.cs.  of  water  and  the  same  quantity  of  ice,  with  950  c  cs 
good  stirring,  during  5  minutes.  The  mixture  becomes  very  hot, 
and  the  temperature  is  accurately  followed  with  the  thermometer, 
the  rate  of  addition  being  such  that  the  end  volume  will  be  exactly 
2600  c.c.  and  the  temperature  60°  ;  this  is  easily  done  with  a  little 
practice. 

1  The  sodium  salt  of  the  2:5  acid  is  easily  soluble  in  95  %  alcohol,  whilst 
those  of  the  2:7  and  2:8  acids  are  soluble  with  difficulty  ;  cf.  D.  R.  P.  39925 
and  29084. 


38  INTERMEDIATE  PRODUCTS 

The  reason  why  these  and  similar  figures  must  be  so  carefully 
observed  lies  in  the  following  :  If  the  temperature  rises  too  high, 
the  naphthylamine  disulphonic  acid  2:1:5  decomposes  and  splits 
off  a  sulphonic  group  ;  the  2:5  acid  then  precipitates  out  and 
carries  other  acids  down  with  it.  If  the  temperature  is  too  low,  the 
naphthylamine  disulphonic  acid  2:5:7  separates  out,  which  is  also 
undesirable. 

The  mixture  is  now  allowed  to  cool  down  to  40°  with  continuous 
stirring.  The  vessel,  which  must  not  crack,  is  placed  in  warm 
water.  Within  5  hours  the  hydrate  of  the  naphthylamine  disulphonic 
acid  will  have  separated  out  in  a  completely  pure  form,  whilst  all 
the  remaining  sulphonic  acids  stay  in  solution.  It  is  then  filtered 
off  quickly  through  as  large  a  "  nutsch  "  as  possible,  fitted  with 
a  good  double  filter  paper,  so  as  to  prevent  the  solution  from 
cooling  too  rapidly.  The  press-cakes,  which  have  a  sulphuric 
acid  content  of  about  35  %,  are  well  pressed  with  a  screw-press 
and  the  filtrate  united  with  the  other  filtrates  :  Press-cake  I. 
(about  200  gms.). 

During  the  course  of  the  next  day  a  completely  pure  naphthyl- 
amine disulphonic  acid  2:5:7  separates  out  at  15°,  which  again  is 
filtered  off  and  pressed  :  Press-cake  II.  (about  70  gms.). 

The  filtrate  from  this  second  crystallization  is  exactly  neutralized 
with  chalk,  as  described  under  H-acid  (pp.  15-16),  converted  into 
the  sodium  salt  by  the  addition  of  the  necessary  quantity  of  soda, 
and  the  filtered  liquid  evaporated  down  to  750  c.cs.  After  standing 
several  days  the  sparingly  soluble  sodium  salt  of  naphthylamine 
disulphonic  acid  2:1:5  separates  out  and  is  filtered  off  and  dried  : 
Press-cake  III.  (about  70  gms.  dry  substance). 

The  solution  freed  from  the  2: 1:5  salt  is  now^evaporated  down 
ca.  25  c.cs.       further  to  |  a  litre,  and  is  then  acidified  with  25  c.cs.  of  hydrochloric 
30  %  HC1.       acid.     Again   a   practically   pure   naphthylamine   disulphonic   acid 
2:5:7  separates  out :  Press-cake  IV.  (about  45  gms.). 

Press-cake  I.  (about  200  gms.  dry  substance)  is  dissolved  in 

700  c.c.  700  c.c.  of  water  at  100°  and  treated  with  70  gms.  of  salt.     The 

Water.  monosodium  salt  of  the  pure  naphthylamine  disulphonic  acid  2:6:8 

NaCl.  separates  out  to  such  an  extent  that  the  contents  of  the  vessel  become 

solid.     The  cakes  are  crushed,  filtered  after   12  hours,  and  well 

pressed.     The  dry  substance  weighs  about  145  gms.  and  titrates  about 

29  gnis.  nitrite.     Similarly  with  press-cakes  II.  and  IV.,  which  are 

dissolved  in  about  five  times  their  weight  of  boiling  water  and 

precipitated  with  half  their  weight  of  common  salt.     Total  yield 

about  ico  gnis.  (=21  gms.  nitrite). 


PLATE   IV. 


SULPHONATIONS  39 

The  2:1:5  acid  titrates  at  about  3*5  gms.  nitrite ,  and  is  very 
impure  owing  to  the  presence  of  other  salts.  The  various  mother- 
liquors  are  kept  separately,  they  titrate  about  n  gms.  nitrite,  but 
cannot  be  fractionated  in  the  laboratory. 

The  pure  sulphonic  acids  are  distinguished  by  a  very  character- 
istic  fluorescence,  which  can,  however,  only  be  seen  clearly  with 
very  pure  products,  as  otherwise  they  are  hidden  by  the  fluorescence 
of  the  2:6:8  acid.  The  2:6:8-naphthylamine  disulphonic  acid 
fluoresces  blue,  the  2:5:7  acid  green,  and  the  2:1:5  acid  red. 
Further,  the  2:6:8  and  2:5:7  acids  show  a  different  behaviour 
with  an  acetic  acid  solution  of  diazotized  nitraniline  ;  the  2:6:8 
acid  gives  only  a  faint  yellowish  coloration  in  dilute  solution  due 
to  the  formation  of  a  diazoamino  compound,  whilst  the  2:5:7  acid, 
on  the  contrary,  yields  at  once  a  true  red  azo  colour.  It  is  therefore 
possible  to  gain  an  idea  as  to  the  purity  of  the  products  from  the 
intensity  of  the  colorations.  Again,  the  diazotized  2:6:8  acid 
forms  a  very  difficultly  soluble  red  azo  dye  with  R-salt  which  is 
precipitated  at  once  even  at  great  dilution  and  dissolves  with  a  red 
colour  on  boiling,  whilst  the  2:5:7  acid  gives  an  orange-red  dye 
which  is  easily  soluble. 

Notes  on  Works  Technique  and  Practice. — The  addition  of  soda 
to  the  substance  which  is  to  be  sulphonated  is  made  solely  for  the 
purpose  of  preventing  the  formation  of  lumps  on  mixing  with 
sulphuric  acid  ;  the  mixture  is  broken  up  by  the  carbonic  acid  given 
off  and  very  small  quantities  of  soda  suffice.  In  the  factory  the 
process  is  often  carried  out  somewhat  differently  from  that  given 
above.  Instead  of  sulphonating  with  monohydrate,  the  sulphate 
or  the  free  ^3-naphthylamine  base  is  added  directly  to  40  %  oleum. 
Also  less  monohydrate  is  used  as  a  diluent ;  the  reasons  for  this  are 
the  same  as  those  already  given  (cf.  p.  n).  In  a  well-conducted 
works  the  isolation  of  the  various  sulphonic  acids  is  comparatively 
easy,  as  the  individual  acids  can  be  better  separated  when  working 
with  large  quantities  than  in  the  laboratory.  Filtration  is  usually 
carried  out  by  means  of  wooden  filter-presses  fitted  with  so-called 
nitro-filters  (q.v.).  The  purified  acids,  or  their  acid  salts,  may  be 
centrifuged  with  advantage.  The  various  mother-liquors,  which 
on  the  laboratory  scale  contain  an  inseparable  mixture  of  acids,  are 
worked  up  either  separately  or  mixed  together  according  to  the 
degree  of  purity.  For  this  purpose  they  are  neutralized  completely 
with  soda  and  "  evaporated  down  to  salt"  that  is  to  say,  they  are 
evaporated  down  in  a  multiple-effect  vacuum  concentrator  until  the 
sparingly  soluble  sodium  chloride  is  precipitated  out ;  the  latter  is 


4o 


INTERMEDIATE  PRODUCTS 


35  gms. 
Nitrite. 
2:8:6- 
Naphthyl- 
amine  disul- 
phonic  acid. 
ca.  180  gms. 
220  gms. 
NaOH. 
1 20  gms. 
H20. 


then  always  centrifuged  and  the  mother-liquors  returned  to  the 
process.  It  is  found  that  during  the  sulphonation  a  certain  amount 
of  diazotizable  nitrogen  always  disappears  ;  this  is  to  be  attributed 
partly  to  the  direct  combustion  of  the  substance,  and  partly  to  the 
formation  of  very  easily  soluble  sulphones  or  sulphamides,  the 
presence  of  which  is  readily  noted  owing  to  their  yellow  colour. 

The  2:5:7  and  2:6:8  acids  are  melted  with  caustic  soda  to 
the  corresponding  aminonaphthol  sulphonic  acids,  or,  more  rarely, 
they  are  sulphonated  further.  The  2:1:5  acid,  however,  is  either 
worked  up  directly  to  light-resistant  azo  colours  of  the  Lithol  Red 
type,  or  it  is  sulphonated  a  stage  further  and  is  then  fused  to  give 
aminonaphthol  disulphonic  acid  2:5:1:7. 

The  total  yield  of  titratable  naphthylamine  disulphonic  acids  is 
very  satisfactory.  Approximately  the  following  quantities  are 
obtained  from  i  molecule  of  j8-naphthylamine  or  from  the  corre- 
sponding quantity  of  jS-naphthylamine  sulphate  : 

i  Molecule  (=69  gms.  sodium  nitrite)  yields  about 

29  nitrite  as  2:6:8-naphthylamine  disulphonic  acid 


20 

3*5 
ii 


2:57 
2:1:5 


two 

separate 
fractions. 


as  residual  acids =mixture  of  various  isomers. 


Total=63'$  nitrite  as  definite  disulphonic   acids=^2  %  of  theory. 
Products  equivalent  to  about  3*5   nitrite  remain  un- 
accounted for . 


Aminonaphthol  Sulphonic  Acid  2:8:6  (y-Acid).    M.W.  239. 

OH 


HO,S'6 


The  melt  of  the  pure  naphthylamine  disulphonic  acid  offers  no 
special  difficulties  so  long  as  the  acid  is  as  free  as  possible  from 
sodium  chloride  (cf.  p.  22). 

A  quantity  of  naphthylamine  disulphonic  acid  2:6:8  equivalent 
to  35  gms.  nitrite  (either  the  pure  dry  substance  or  the  corresponding 
amount  of  moist  acid)  is  heated  with  220  gms.  of  chlorate-free 
caustic  soda  and  120  gms.  of  water  in  a  stirring  autoclave  during 
7  hours  at  205-210°,  the  pressure  rising  to  14  atmospheres.  After 
cooling  and  releasing  the  pressure  the  contents  of  the  autoclave  are 
diluted  up  to  i  litre  (N.B.  the  melt  should  not  smell  strongly  of 


SULPHONATIONS  41 

ammonia),  and  concentrated  sulphuric  acid  is  added  until  distinctly  250  gms. 
mineral  acid,  about  250  gms.  cone,  sulphuric  acid  being  required  conc-H2SO4. 
for  this  purpose.     After  standing  a  few  hours  the  Gamma-acid  is 
filtered  off  and  well  washed  with  cold  water,  in  which  it  is  very 
sparingly  soluble  ;  the  cake  is  then  pressed  and  dried  at  100°. 

Yield :  About  105  gms.  (=95  gms.  of  100  %  product)  Gamma-acid 
from  "  35  gms.  nitrite,"  or  approximately  80  %  of  theory.  The  acid 
is  estimated  by  coupling  with  Normal  diazotized  aniline  in  dilute 
strongly  alkaline  solution,  and  simultaneously  in  another  sample  by 
diazotizing  in  very  dilute  mineral  acid  solution  (for  general  details 
as  to  this  type  of  estimation  see  Analytical  Section).  The  figures 
obtained  for  the  two  estimations  should  agree  within  i  %,  as  in  the 
case  of  H-acid.  If  the  melt  has  been  carried  out  at  too  low  a  tem- 
perature the  nitrite  number  will  be  greater  than  the  coupling  figure. 
The  y-acid  should  be  at  least  91  %. 


Aminonaphthol  Sulphonic  Acid  2:5:7 
(J-Acid,  iso-y-Acid).     M.W,  239. 


The  method  is  exactly  the  same  as  for  Gamma-acid,  except  that  35 
preferably   somewhat   more   water   is   used   for   the   melt,   namely 
1 60    gms.  instead   of    120,  and  further  the  temperature  is  a  trifle  Naphthyl- 
lower,  200-205°  for  7  hours.  ZntclSd.' 

The  yield  is  about  the  same  as  in  the  case  of  y-acid,  i.e.  about  95  ca.  180  gms. 
gms.  of  100  %  aminonaphthol  sulphonic  acid  2:5:7  (=circa  io$gms.  at  NaO??8 
92%)  or  82  %  of  theory.     The  yield  of  2:5:7~acid  is  therefore  a   1 60  gms. 
trifle  better  than  that  for  y-acid.  Ha°' 


Nitrobenzene   Sulphonic   Acid   and   Metanilic   Acid   from 

Nitrobenzene. 
Reaction  : 

NO2  NO2  NO2  NO2 


«!S08H  +  a  little  I     ^-S02-|s 


Sulphone. 
i   Gm.-molecule  of  nitrobenzene  is  allowed  to  run  cautiously 


42 


INTERMEDIATE  PRODUCTS 


123  gms. 
Nitroben- 


375 
Oleum 

(25  %). 


500  gms. 
Ice. 


200  gms, 
Salt. 


250  gms. 
Iron  Powder 
400  c.cs. 
Water. 


ca,  100  c.cs. 
HC1  (30  %) 
and,  if 
necessary, 
100  gms. 
NaCl. 


into  three  times  the  quantity  of  oleum  (25  %  SO3)  at  70°,  contained 
in  a  cast-iron  pot  similar  to  that  used  for  the  sulphonation  of  the 
naphthalene  sulphonic  acid  The  mixture  warms  up  rapidly  to 
1 00-110°,  but  must  not  be  allowed  to  rise  any  higher,  or  else  there 
is  danger  of  sudden  carbonization.  When  all  has  been  added,  the 
mixture  is  heated  at  110-115°  until  a  test  portion  poured  into  water 
no  longer  gives  any  odour  of  nitrobenzene.  If  complete  sulphona- 
tion has  not  occurred  within  half  an  hour  of  the  mixing,  then  insuffi- 
cient SO3  has  been  used.  In  this  case  50  gms.  more  oleum  are 
added  drop  by  drop,  and  if  necessary  a  further  quantity  after 
half  an  hour  more,  but  if  the  oleum  used  really  contained  25  %  SO3 
no  more  tnan  the  original  quantity  will  be  required.  The  mixture  is 
then  allowed  to  cool,  and  is  poured  on  to  500  gms.  ice  with  good 
mechanical  stirring.  The  nitrobenzene  sulphonic  acid  goes  com- 
pletely into  solution  with  the  exception  of  a  small  proportion  of 
sulphone. 

The  further  working  up  of  the  acid  may  be  effected  in  various 
ways,  e.g.  as  given  under  H-acid  on  pp.  15—20.  '  The  method 
recommended  is  to  salt  out  the  acid,  as  the  sodium  salt  is  practically 
insoluble  in  saturated  brine  ;  200  gms.  common  salt,  in  small  quan- 
tities at  a  time,  are  slowly  sprinkled  in  with  continuous  stirring. 
The  sodium  salt  of  nitrobenzene  sulphonic  acid  separates  out  as  -a 
thick  paste,  and  stirring  must  be  continued  for  some  time,  until 
the  mass  again  liquefies.  After  about  10  hours  the  solid  is  filtered 
off  through  paper  on  a  large  suction  funnel,  and  is  then  well  pressed 
(in  cotton  cloth)  in  a  screw-press.  The  sodium  salt  can  be  used 
technically  without  further  treatment,  or  may  be  obtained  pure  by 
recrystallizing  from  water. 

The  reduction  is  carried  out  as  described  for  H-acid,  with  the 
one  difference  that  the  iron  used  need  not  be  subjected  to  a  pre- 
liminary "  etching,"  as  the  free  acid  contained  in  the  press-cake  is 
sufficient  to  start  the  reaction.  The  reduction  product  is  then 
neutralized  and  filtered,  as  described  on  p.  18.  On  evaporating 
down  to  600  c.cs.  and  acidifying  the  solution  with  hydrochloric  acid 
until  acid  to  Congo,  the  metanilic  acid  comes  out  as  a  finely  crystalline 
precipitate.  Many  works  prefer  to  use  the  concentrated  solution 
directly,  as  the  metanilic  acid  is  extremely  soluble,  and  10-15  %  is 
always  lost  on  separating  out,  although  this  loss  is  more  than  made 
up  for  by  the  higher  yield  of  finished  dye.  The  yield  is  determined 
by  simply  titrating  the  mineral  acid  solution  with  sodium  nitrite, 
and  is  about  90  %  =  approximately  140  gms.  of  100  %  product. 

Other     similar    Sulphonations. — The    following    substances    are 


SULPHONATIONS  43 

sulphonated  in  similar  manner  to  the  foregoing,  ^-nitro-chlorbenzene, 
^>-nitro-toluene,  o-nitro-chlorbenzene,  chlorbenzenes,  etc.  Dinitro 
bodies,  on  the  other  hand,  cannot  be  sulphonated  in  this  way. 
Dinitrochlorbenzene,  on  treatment  in  this  way  with  fuming 
sulphuric  acid,  decomposes  with  explosive  violence,  as  do  the 
dinitro-toluenes.  If  it  be  desired  to  prepare  dinitrochlorbenzene 
disulphonic  acid,  for  example,  one  starts  with  ^-nitrochlorbenzene  : 
this  is  sulphonated  according  to  the  above  method,  and  the  sulphonic 
acid  then  converted  into  the  dinitrochlorbenzene  sulphonic  acid  by 
means  of  50  %  mixed  acid  (50  %  H2SO4-f  50  %  HNO3)  at  a  low 
temperature  ;  it  has,  however,  no  technical  importance.  Dinitro- 
naphthalenes  are  converted  into  naphthazarine  on  treatment  with 
oleum. 

Notes  on  Works  Technique  and  Practice. — Sulphonations  similar 
to  the  foregoing  are  carried  out  on  the  works  scale  in  steam-jacketed 
vessels  through  which  either  steam  or  cold  water  may  be  allowed  to 
flow.  The  substances  frequently  heat  up  very  considerably,  so  that 
it  is  necessary  to  use  caution  in  working,  as  otherwise  dangerous 
rises  in  temperature  and  even  explosions  may  take  place.  The 
salting  out  is  done  in  wooden  vats,  the  pressing  of  the  filter  cakes 
being  effected  first  in  filter-presses  and  then  (in  hair  cloths)  in 
hydraulic  presses  at  250  atmospheres.  The  reduction,  evaporation, 
and  further  working  up  are  carried  out  as  already  described. 


Sulphanilic  Acid. 
Bake  Process. 

So  far  we  have  only  examined  cases  of  sulphonation  where  the 
liquid  was  kept  in  motion  by  means  of  a  stirrer.  There  is,  however, 
another  method  of  sulphonating,  which  is  based  on  a  quite  different 
idea  ;  certain  substances  sulphonate  when  their  acid  sulphates  are 
heated  to  moderate  temperatures.  This  method  obviously  applies 
only  to  bases,  such  as  aniline,  whilst  benzidine  and  more  complicated 
bases,  such  as  dehydro-thiotoluidine,  give  by  this  method  different 
isomers  from  those  obtained  with  the  liquid  acid. 

This  reaction  is  usually  referred  to  as  the  Bake  Process >  as  the  acid 
sulphates  are  heated  on  tin  trays  like  baking 'tins  to  moderately 
elevated  temperatures. 

It  is  sufficient  to  heat  the  dry  acid  sulphates  in  thin  layers  at 
170-210°  for  5-10  hours  in  order  to  obtain  practically  quantitative 
yields  of  the  desired  sulphonic  acids.  The  most  favourable  tem- 
perature must,  of  course,  be  first  determined  in  each  case.  Again, 


44  INTERMEDIATE  PRODUCTS 

certain  bases,  such  as  benzidine,  toluidine,  etc.,  carbonize  very  easily 
if  any  excess  of  sulphuric  acid  be  taken,  particularly  in  the  presence 
of  air  ;  further,  sulphones  and  disulphonic  acids  may  be  formed  as 
well.  In  modern  factories,  therefore,  the  heating  is  carried  out 
in  vacuo,  the  sulphonation  then  going  more  smoothly  and  more 
quickly.  The  ovens  used  for  this  reaction  are  either  directly  heated 
with  fire,  or,  better,  with  superheated  steam.  Electrical  heating  may 
also  be  employed,  and  has  the  advantage  of  easy  regulation,  besides 
avoiding  the  necessity  for  using  thick  boiler-plates. 


Reaction  : 


NH 


NH, 


NH 


HSO4    ->  +H2O 


-]-H2S04 


105  gms.  Sulphanilic  Acid. — 105  gms.  (=i  gm.-molecule)  of  66°  Be.  sul- 

66°SB64'  Pnuric  acid  is  mixed  with  93  gms.  aniline  (=i  gm.-molecule)  in  an 

93  gms.  iron  basin,  the  base  being  placed  in  the  vessel  and  the  sulphuric 

Aniline.  ^jd  added  in  a  thin  stream  with  good  stirring.     In  the  factory  it  is 

done  in  an  iron  pot,  and  may  be  worked  over  with  an  iron  rake. 
The  resultant  thick  paste  is  at  once  spread,  whilst  still  hot,  on  iron 
trays  (15X15  cms.),  furnished  with  rims  2  cms.  deep.  The  layer 
should  be  about  i  cm.  thick  (8  cms.  on  the  large  scale),  and  the 
trays  are  then  placed  in  the  drying  chest  at  least  5  cms.  from  the 
heating  surface,  the  latter  being  heated  by  means  of  a  Bunsen  burner 
fitted  with  a  "  mushroom  "  top  ;  the  mass  is  heated  for  8  hours  at 
190°.  The  cakes  are  then  removed  from  the  oven  and  the  resultant 
sulphanilic  acid  shaken  out  of  the  tin.  It  is  about  90  %  pure  and 
pale  grey  in  colour  ;  in  addition  to  sulphanilic  acid  it  contains  about 
3  %  of  unchanged  aniline  and  a  little  free  carbon.  For  many 
purposes  this  crude  sulphanilic  acid  may  be  used  directly  by  dis- 
solving in  sufficient  soda  to  give  a  strong  blue  coloration  with 
60  gms.  litmus,  in  the  present  case  some  60  gms.  soda  and  500  c.cs.  water 

soo2gms          being  required.     The  liquid  is  heated  to  boiling,  water  being  added 
H2O.  to  balance  evaporation,  until  the  steam  has  removed  the  easily 

volatile  aniline.  It  is  then  run  through  a  cotton  filter,  and  the 
solution  contains  a  sulphanilic  acid  which  will  answer  most  of  the 
technical  requirements  without  further  treatment.  In  order  to 
obtain  pure  sulphanilic  acid  from  the  solution  it  is  acidified  with 
sulphuric  acid  until  acid  to  Congo  paper.  The  sulphanilic  acid  is 


SULPHONATIONS  45 

precipitated  in  a  very  pure  form  which  is,  however,  not  adequate  for 
analytical  purposes  (cf.  Analytical  portion). 

The  yield  of  crude  substance  is  approximately  175  gms.,  or  about 
140  gms.  of  purified  reprecipitated  acid, 

Naphthionic  acid  (naphthylamine  sulphonic  acid  1 14)  may  also  be 
prepared  by  the  baking  process  in  a  similar  manner.  In  this  case, 
however,  the  sulphonation  and  further  working  up  will  not  go  so 
smoothly  ;  from  5-10  %  of  the  naphthylamine  always  remains 
unchanged  but  cannot,  of  course,  be  removed  simply  by  distilling 
off  with  the  water  as  in  the  case  of  sulphanilic  acid.  Further,  the 
unchanged  base  cannot  be  removed  by  filtering  the  sodium  naph- 
thionate  solution  as  the  base  emulsifies  in  the  solution  of  the  salt 
and  goes  through  all  forms  of  filter.  It  is  therefore  necessary  to 
dissolve  the  crude  acid  in  alkali  and  to  remove  the  naphthylamine 
by  treating  the  alkaline  solution  with  benzene  in  an  extraction 
apparatus.  A  further  drawback  is  that  a  certain  quantity  (3-7  %) 
of  the  1:5  acid  is  always  produced  together  with  the  1:4  acid.  This 
so-called  Laurent's  acid  can  only  be  removed  by  crystallizing  out 
the  naphthionate,  for  which  reason  the  naphthionic  acid  is  always 
dealt  with  as  its  sodium  salt  (naphthionate). 


Other  Methods  of  Sulphonation. 

In  addition  to  sulphuric  acid  certain  other  sulphonating  agents 
may  be  made  use  of,  although  they  play  no  very  important  part  in 
dye  technology.  The  use  of  chlor-sulphonic  acid  as  a  sulphonating 
agent  will  not  be  discussed  here,  as  it  is  only  employed  in  very  special 
cases.  Its  application  to  the  preparation  of  the  acid  chlorides  of 
the  toluene  sulphonic  acids  may  be  referred  to  ;  these  may  be 
prepared  in  the  same  apparatus  as  already  described  for  other 
sulphonations.  In  addition  to  its  use  for  the  preparation  of  sulphonic 
chlorides  chlor-sulphonic  acid  is  still  employed  for  the  sulphonation 
of  certain  azo  colours,  as  it  forms  a  very  mild  non-oxidizing  sul- 
phonating medium,  but  it  cannot  be  used  for  the  sulphonation  of 
bases  ;  amino  groups  inhibit  its  action  at  lower  temperatures  so 
that  it  is  more  advantageous  to  use  sulphuric  acid  or  oleum.  Hydroxy- 
lated  compounds  do  not  yield  the  sulphonic  chlorides  of  the  phenols 
or  naphthols,  but  give  the  corresponding  free  sulphonic  acids 
directly. 

Bisulphite  and  neutral  sulphite  may  also  be  used  under  certain 
conditions  for  introducing  a  sulphonic  group.  This  method  of  intro- 
ducing a  sulphonic  group  into  an  aromatic  nucleus  was  first  employed 


46 


INTERMEDIATE  PRODUCTS 


202  gms. 

Dinitro- 

chlor- 

benzene. 

500  gms. 

90  %  Alcohol. 

80  gms. 

320  gms. 
NaHSO3. 
25  %  SO2. 
ca.  100  gms. 
40  %  NaOH. 


by  Nietzki  (D.  R.  P.  89097).  Thus  nitraniline  sulphonic  acid 
3:1:4  may  be  obtained  by  the  action  of  sodium  sulphite  upon 
dinitro-benzene  but  in  poor  yield,  and,  so  far  as  is  known,  this  is 
not  made  use  of  practically. 


Reaction  : 


NO2 

x\ 


N0< 


+2Na2S03 


NH2 

A 

N02 
S03H 


More  important  is  the  introduction  of  the  sulphonic  group  by 
replacing  an  easily  removable  chlorine  atom  with  the  aid  of  neutral 
sodium  sulphite,  as  was  proposed  by  Erdmann  in  D.  R.  P.  65240. 
By  a  slight  modification  of  this  interesting  process  it  is  possible  to 
improve  the  yield  considerably. 


m-Phenylenediamine  Sulphonic  Acid  1:2:4. 


Reaction  : 
Cl 


\y 

NO2 


+Na2SO3    -> 


SO3Na 
^,N09 


S0H 


NO. 


NH 


202  Gms.  dinitro-chlor-benzene  (=  i  molecule)  are  mixed  with 
500  gms.  of  methylated  spirits  which  must  not  have  been  denatured 
with  pyridine  bases.  (Caution  is  necessary  owing  to  the  unpleasant 
properties  of  dinitro-chlor-benzene.)  To  this  is  added  80  gms. 
SO2  (=i  molecule)  in  the  form  of  a  concentrated  solution  of  sodium 
sulphite.  This  concentrated  solution  is  prepared  from  the  com- 
mercial sodium  bisulphite  solution  by  the  addition  of  the  exactly 
equivalent  quantity  of  strong  soda  lye.  40  %  Caustic  soda  is  added 
until  phenolphthalein  paper  is  just  faintly  reddened.  The  sulphite 
separates  out  to  a  certain  extent  even  whilst  warm,  but  this  is  of 
no  consequence.  The  mixture  of  dinitro-chlor-benzene,  sulphite, 
water,  and  spirit  is  now  heated  on  the  water-bath  to  boiling  during 
5  hours,  with  good  stirring  (Fig.  9,  p.  47).  The  product  is  then 
cooled  down  as  far  as  possible  by  standing  in  cold  water,  when  the 
sodium  salt  of  the  dinitro-benzene  sulphonic  acid  separates  out  in 
beautiful  glistening  yellow  leaflets. 


SULPHONATIONS 


47 


If  the  process  be  carried  out  exactly  in  accordance  with  the 
patent  very  unsatisfactory  results  will  be  obtained  as,  according  to 
this,  the  alcohol  is  simply  distilled  off.  It  is  far  better  to  filter 
off  the  separated  product  on  a  nutsch,  and  to  press  out  the  mass 
in  a  screw-press.  The  leaflets  of  the  sodium  salt  are  then 
reduced  exactly  as  given  f  for  the  reduction  of  dinitro-benzene 
(q,v.).  The  solution  of  the  m-phenylenediamine  sulphonic  acid  is 


not,  however,  sufficiently 

pure  for  the  purposes  of 

the  azo  colour  industry. 

It  is  therefore  necessary  I?°rgms- 

to    evaporate    down    the  cat  I0'0  gms> 

solution     to     about     400  HC1>  30  %. 

and  to  add  100 
gms.  common  salt ;  on 
acidifying  with  hydro- 
chloric acid  the  free  sul- 
phonic acid  comes  out  in 
fine  crystals.  It  is  very 
important  that  just  the 
right  quantity  of  acid  be 
taken,  as  the  sulphonic 
acid  will  redissolve  in 
any  excess  ;  Congo  paper 
should  not  be  turned 
pure  blue,  but  just  a  definite  faint  violet.  After  two  days  the 
product  is  filtered  off  and  washed  in  a  very  little  water. 

The  yield  is  about  125  gms.  pure  substance,  or  about  66  %  of 
theory. 

Notes  on  Works  Practice. — Reactions  of  this  type  are  best  carried 
out  in  homogeneously  lead-lined  iron  boilers  (q.v.).  It  is  very 
important  that  no  trace  of  any  other  metal  should  come  in  contact 
with  the  liquid.  A  few  milligrams  of  copper  or  iron  suffice  to 
prevent  any  trace  of  the  desired  compound  being  obtained.  The 
dinitro-benzene  sulphonic  acid,  as  also  the  finished  w-phenylene~ 


FIG.  9. — Heating  under  reflux  condenser  with 
stirring. 


48 


INTERMEDIATE*  PRODUCTS 


diamine  sulphonic  acid,  is  best  not  filtered  off  in  a  filter-press, 
but  is  centrifuged  instead.  The  remainder  of  the  alcohol  is  removed 
by  hydraulic  pressing,  and  after  rectifying  in  a  spirit  column,  may 
be  used  again  ;  with  careful  working  not  more  than '5  %  of  the 
alcohol  should  be  lost  during  the  whole  operation. 

The  mobility  of  the  chlorine  atom  in  negatively  substituted 
aromatic  hydrocarbons  is  frequently  made  use  of  for  the  synthesis 
of  important  dye  intermediates.  Further,  actual  dyes,  particularly 
those  of  the  anthraquinone  series,  may  be  produced  by  the  aid  of 
this  reaction.  Colouring  matters  cannot  be  discussed  here  in  this 
connection,  but  a  few  interesting  intermediate  products  obtained  in 
this  manner  will  now  be  described. 


ioo  gms. 
p-Nitro- 
chlor- 
benzene. 
ioo  gms. 
H2S04, 
ioo  %. 
280  gms. 
Oleum, 
25  %• 


p-Nitraniline  Sulphonic  Acid  from  />-Nitro-chlor-benzene. 
Reaction  : 

Cl  Cl  NH2 

I  /?\S03H(NH3) 

\4/ 

NO, 


N0 


A 

NO< 


The  sulphonation  of  />-nitro-chlor-benzene  is  effected  in  a  very 
similar  manner  to  that  of  nitro-benzene.  Thus,  for  example,  ioo 
gms.  ^>-nitro-chlor-benzene  are  mixed  with  ioo  gms.  of  sulphuric 
acid  monohydrate  at  50°,  and  to  this  are  added,  with  stirring,  280  gms. 
of  oleum  containing  25  %  SO3.  The  product  is  then  warmed  to 
100-110°  until  the  nitro-chlor-benzene  has  disappeared.  The 
mixture  is  poured  on  to  300  gms,  of  ice  and  300  gms.  of  water 
and  is  salted  out  with  200  gms.  of  common  salt  ;  after  24  hours  the 
product  is  filtered  off  and  pressed.  The  yield  is  about  280  gms. 
moist  press-cakes.  The  cakes  are  then  broken  up  and  heated  with 
their  own  weight  of  strong  ammonia  (20  %  NH3)  in  autoclaves 
at  150°  during  8  hours,  in  order  to  obtain  the  ^-nitraniline  sulphonic 
acid.  The  pressure  rises  to  about  6  atmospheres  (steel  tube  mono- 
meter).  On  cooling,  the  ammonium  salt  of  the  desired  sulphonic 
acid  separates  out  in  large,  hard,  amber-coloured  cubes,  which  weigh 
about  ioo  gms.  when  isolated.  On  the  large  scale  the  mother-liquor 
from  the  ammonium  salt  is  worked  up  by  means  of  lime  to  recover 
the  ammonia.  f  *i 

The  />-nitro-chlor-benzene  sulphonic  acid  finds,  in  addition,  an 
extensive  application  in  the  preparation  of  diamino-diphenylamine 


SULPHONATIONS 


49 


sulphonic  acid,  and  also  of  amino-diphenylamine  sulphonic  acid. 
The  following  schemes  will  indicate  their  modes  of  formation  : 
i.  Diamino-diphenylamine  sulphonic  acid. 


Cl 

/*\ 

\  4/ 

NO2 


Cl 


NH 


-|- 


j 

NO 


and  MgO  (or  CaC03)  in 

boiling   aqueous   solution. 

(Wooden  tubs.) 


NH2 

p-Phenylene-diamine. 


NH 


NH 


Chief 
reaction 

OBechamp 
reduction 
~* 

NH 

i 

E: 

NH 

i 

1 
r          >Q/"\   T  T 

i  ovvoJrl. 

1         1        3 

i 

rSsn 

u 

3H 

\/ 

NO2 

\/ 

NH2 

N02 

P: 

NH2 

S03H 

NH 

i 

i80 

NH 

1 

3H 

Side  reaction. 

{\ 

0' 

r>pai 
sa 

^^ 

1                           -> 

Y 

Easily  soluble  sodium 


I. 


Diamino-diphenyl- 
amine  sulphonic  acid. 


II. 


Sparingly  soluble  sodium 
salt;  easy  separation. 


NH 


NH 


S03H 


The  intermediate  product  (I.)  gives  valuable  dark  azo  colours 
for  cotton  when  combined  with  amino-naphthol  sulphonic  acids. 


50  INTERMEDIATE  PRODUCTS 

2.  Amino-diphenylamine  sulphonic   acid   (III.)  or   amino-phenyl- 
tolyl  amine  sulphonic  acid. 


/\ 

u 


+  Aniline  (orortho- 
SOoH    toluidine     at    140°;        '„ 
3         stirrin         MO 


NO. 


stirring;     MgO    + 
water) 


iSOoH 


Amino-diphenylamine 
sulphonic  acid. 

Substances  of  this  type  (III.)  yield  the  Nerols  of  the  Berlin 
Aniline  Co.,  which  are  disazo  dyes  obtained  by  coupling  with 
a-naphthylamine  and  subsequent  further  coupling  with  Schaffer  salt 
or  with  other  azo  components. 

We  may  note  here  that  not  only  halogen  atoms,  but  also  nitro 
groups  and  sulphonic  groups  may  be  replaced  by  phenyl-  or  aryl- 
amines.  In  the  anthraquinone  molecule  in  particular  the  easy 
replaceability  of  the  nitro  groups  makes  it  possible  to  obtain  important 
derivatives  in  this  manner,  but  we  cannot  enter  into  this  question 
here.  The  use  of  various  highly  nitrated  benzene  derivatives  also 
gives  rise  to  interesting  condensation  products. 


ioo  gms. 
£-Naphthol. 

90  gms. 
NaOH 

(35  %)• 

i  litre  H2O. 


220  gms. 
H2SO4 
(40  %). 


Preparation  of  an  Amino=naphthol  sulphonic  acid  from  the  corre* 
sponding  hydroxy-nitroso  compound  (Quinone  Monoxime) : 

i:2:4-Amino-naphthol  Sulphonic  Acid  from  ^-Naphthol. 

i.  Nitroso-f$-naphthol. — ioo  gms.  of  jS-naphthol 1  are  dissolved 
in  90  gms.  of  35  %  caustic  soda  lye  and  i  litre  of  water  at  50°,  con- 
tained in  a  glass  jar  of  3  litres  capacity.  To  this  solution,  which 
should  react  faintly  but  distinctly  to  thiazole  paper,  50  gms.  of 
ioo  %  sodium  nitrite  are  added,  and  the  mixture  made  up  with 
water  and  ice  to  2  litres,  temperature  o°.  About  220  gms.  of  40  % 
sulphuric  acid  are  then  allowed  to  run  into  this  with  good  stirring 
during  3  hours  ;  at  the  end  of  the  time  the  solution  should  be 
distinctly  acid  to  Congo  and  should  react  with  nitrite  paper.  After 

1  A  gm. -molecule  is  not  taken  a!  this  would  need  too  great  a  volume  of  liquid. 


SULPHONATIONS 


10  hours  the  nitroso-naphthol  is  filtered  off  on  a  big  porcelain 
filter  and  is  well  washed.  It  is  chemically  pure,  assuming  that  the 
original  /3-naphthol  was  also  pure. 

2.  Reduction  and  Conversion  into  the  Amino-naphthol  Sulphonic 
Acid. — The  still  moist  nitroso-naphthol  is  stirred  up  with  a  little 
water  in  a  glass  jar  and  cooled  down  to  5°  with  ice.     To  the  homo- 
geneous paste  is  added  quickly  260  gms.  sodium  bisulphite  solution  26o  gms. 
(about  25  %  SO2).     The  nitroso-naphthol  goes  into  solution  after  ^isUo/P)hite> 
a  short  time,  a  further  small  quantity  of  dilute  caustic  soda  being 
cautiously  added  if  necessary. 

The  solution  contains  some  resinous  constituents,  and  is  there- 
fore filtered.  (By  salting  out  the  hydroxylamine  sulphonic  acid 
which  is  formed,  Alsace  Green  N  or  Dioxine  N  of  commerce  is 
obtained,  a  dye  which  plays  a  certain  part  in  calico-printing,  the  iron 
lake  being  very  fast  to  light.) 

The  volume  of  the  filtered  solution  is  about  ij  litres.     It  is 
placed  in  a  jar  and  is  then  treated  at  25°  with  100  gms.  sulphuric  100  gms. 
acid  (66°Be.)  which  has  been  diluted  with  200  gms.  of  water.     The  ^o8^4.' 
solution  at  the  end  should  show  a  strongly  mineral  acid  reaction.   200  gms. 
After  i  hour  it  is  warmed  to  50°  and  allowed  to  stand  overnight  ;      2 
the  contents  of  the  jar  solidify  to  a  solid  cake  of  free  amino-naphthol 
sulphonic  acid.     This  is  filtered  off  and  thoroughly  washed  out  with 
water.     The  yield  is  about  90  %,  calculated  on  the  fi-naphthol  used. 


NO 


NOH 


Quinone  oxime. 


OH 


v\/ 


SO3H 

"  Dioxine."  Amino-naphthol  sulphonic  acid  1:2:4. 

Amino-naphthols  of  this  type  cannot  be  diazotized  by  the  method 
used  for  other  amines  since,  on  treating  with  mineral  acids  and  sodium 
nitrite,  quinones  are  formed  and  only  traces  of  the  desired  diazo 
compound.  These  diazo  bodies,  however,  may  be  obtained  quanti- 
tatively by  treating  the  free  acid  (as  obtained  after  filtering  off  and 


52  INTERMEDIATE  PRODUCTS 

washing)  in  concentrated  suspension  with  nitrite  in  presence  of  a 
molecule  of  zinc  chloride  or  of  a  very  small  quantity  of  a  copper 
salt.  Both  methods  are  employed,  the  patent  literature  giving  the 
essential  details  (D.  R.  P.  171024  G.). 

Amino-naphthol  sulphonic  acid  1:2:4  is  an  intermediate 
product  for  important  or^o-hydroxyazo  colours  which  were  dis- 
covered simultaneously  by  Kalle,  Geigy,  and  the  B.A.S.F.  When 
coupled  with  naphthols  they  yield  very  fast  blue-black  chrome 
dyes  ;  the  nitro  derivatives  (Sandmeyer-Hagenbach)  are  the  cheapest 
chrome  blacks  for  wool  on  the  market,  and  have  scarcely  been 
surpassed  for  fastness  (Erio  Chrome  Black  T  and  A). 

It  is  also  of  interest  to  notice  that  those  amines  which  are  substi- 
tuted in  the  di-ortho  positions  couple  with  a-naphthol  in  the  ortho- 
position  to  the  hydroxyl.  Thus  from  i:2:4-amino-naphthol  sul- 
phonic acid,  or,  rather,  from  its  diazo  compound  and  strongly 
alkaline  a-naphthol  solution,  the  ortho-hydroxyazo  compound  is 
produced  quantitatively  (Erio  Chrome  Blue-Black  B,  Geigy). 
These  diazo  compounds  are  so  stable  that  they  can  easily  be  nitrated 
in  sulphuric  acid  solution  by  means  of  "  mixed  acid  "  ;  the  nitro 
diazo  compounds  yield  the  Chrome  Blacks  mentioned  above.  Many 
2:6  di-substituted  anilines  also  couple  with  a-naphthol  in  the  ortho 
position  yielding  products  fast  to  alkali,  whilst  from  ortho-hydroxy 
diazo  compounds  and  a-naphthol  chromable  azo  colours  are  formed. 

The  method  of  sulphonation  by  means  of  sulphurous  acid  men- 
tioned above,  is  also  applied  to  the  preparation  of  amino-phenol 
disulphonic  acid  from  nitroso- dimethyl-aniline  and  sodium  bisul- 
phite. During  the  conversion  to  the  disulphonic  acid,  the  dimethyl- 
ammo  group  is  split  off  leading  to  the  formation  of  the  ^-amino- 
phenol  derivative. 

Reaction  : 

N(CH3)2  N(CH3)2  N(CH3)2  OH 

/T\  /I\ 

+NaHS03 

^  93O.H 


NO  N  NH2 

(S03Na)2.  +NH(CH3)2. 

Pure  dimethylamine  is  produced  at  the  same  time,  which  is  a 
commercial  product. 


P  U 


CTJ 

O   C 


.2 


NITRATIONS  AND   REDUCTIONS  53 

2.  NITRATIONS  AND  REDUCTIONS 

Nitrobenzene.1 


Reaction  : 


The  chief  condition  to  be  observed  in  the  manufacture  of  nitro-   100  gms 
benzene  is  the  correct  and  intimate  mixture  of  the  components  ;   if  jfo^s 
this  is  done  it  is  easy  to  obtain  good  yields.    100  Gms.  of  benzene  are  HNO3, 
treated  with  a  mixture  of  no  gms.  nitric  acid  (sp.  gr.  1*44— 44°  Be.)  X^f  gms 
and  170  gms.  concentrated  sulphuric  acid  of  66°  Be.  with  vigorous  HgSO*, 
stirring,  in  a  porcelain  beaker  provided  with  a  well-fitting  lid,  or  in 
a  glass  bolthead  (Fig.  9).     In  order  to  ensure  smooth  nitration  an 
acid  of  sp.  gr.  1*46  (=80  %   HNO3=46°  Be.)  may  be  used,  but  in 
practice  an  "acid  of.  1*44  (=75  %  HNO3)  is  quite  sufficient.     The 
internal  temperature  is  maintained  at  50°  by  external  cooling,  the 
addition  of  the  acid  occupying  about  half  an  hour.     When  all  has 
been  added  the  mixture  is  stirred  for  a  further  2  hours  at  50-60°. 
The  nitrobenzene  floats  on  the  surface  of  the  acid,  which  has  a  specific 
gravity  of  about  1*236.     The  product  is  separated  in  a  separating 
funnel,  washed  with  a  little  water,  then  with  dilute  soda  solution, 
and,  finally,  again  with  water.     It  is  then  tested  with  litmus  and 
distilled.     At  first  a  little  water  and  some  benzene  come  over,  and 
then  pure  nitrobenzene.     If  the  benzene  used  is  pure,  excellent 
yields  should  be  obtained  even  in  the  laboratory,  100  gms.  of  benzene, 
for  example  .yielding  150  gms.  of  pure  nitrobenzene.     B.p.  205°. 

Notes  on  Works  Technique  and  Practice. — Nitrobenzene  is  one 
of  the  most  important  products  used  in  colour  technology.  It 
serves  for  the  preparation  of  aniline  and  benzidine,  and  also  for  the 
production  of  the  important  Nigrosines.  On  the  works  scale  for 
the  production  of  nitrobenzene,  charges  up  to  1500  kgs.  of  benzene 
are  employed,  yields  of  98  %  being  obtained.  With  such  large 
charges  the  operation  lasts  about  12  hours,  about  97  %  of  the  nitric 
acid  being  used  up.  The  course  of  the  reaction  is  usually  followed 
by  a  quantitative  determination  of  the  amount  of  nitric  acid  remaining 
in  the  acid  mixture.  The  waste  acid  should  not  contain  finally 
more  than  i  %  of  nitric  acid  (estimation  in  Lunge  nitrometer). 
The  nitrobenzene  is  usually  used  without  further  purification,  but 
to  obtain  it  in  a  pure  condition  it  is  always  distilled  in  vacuo. 

Figs.  10  and  ii  (Plate  IV.)  show  a  nitrating  vessel  with  internal 

1  Cf.  also  Ullmann,  Enzyklopadie  d.  Techn.  Wissenschaften, 


54 


INTERMEDIATE  PRODUCTS 


123  gms. 

Nitro- 

benzene. 


66°  Be. 
140  gms. 
HN03, 
47°  B6. 


cooling  as  used  for  aromatic  hydrocarbons,  and  also  a  separating 
funnel  with  a  sight  glass  (or  so-called  "  lunette  ")  and  a  lead  or 
stoneware  tap  affixed  beneath.  The  nitrating  plant  for  benzene 
must  be  homogeneously  lead-lined  as  the  waste  acid  obtained  at 
the  end  attacks  iron  owing  to  its  too  great  dilution. 


m-Dinitrobenzene  from  Nitrobenzene. 


Reaction  : 

NO2 


NO, 

r 


NO, 


NO 

ix 


NO2i 


and 


4 

NOc 


i:3-Dinitrobenzene,  usually  referred  to  simply  as  dinitrobenzene, 
is  obtained  from  mono-nitrobenzene.  For  this  purpose  the  crude 
nitrobenzene  is  always  employed.  It  is  only  necessary  to  run  off 
the  waste  acid  after  the  first  mono-nitration  has  been  effected.  It 
is  not  possible  to  treat  benzene  straight  away  with  excess  of  nitric 
acid  as  explosions  may  occur.  It  is  also  absolutely  essential  that  the 
stirring  be  as  vigorous  as  possible,  as  insufficient  mixing  may 
be  extremely  dangerous,  particularly  on  the  large  scale.  If,  owing 
to  the  stopping  of  the  stirrer,  two  layers  should  form,  consisting  of 
hydrocarbon  on  the  one  hand  and  nitrating  acid  on  the  other,  the 
acid  should  at  once  be  run  off  with  the  stirrer  stationary.  Cases 
have  been  known  in  the  industry  where  terrible  explosions  have 
occurred  on  subsequently  restarting  the  stirrer  owing  to  sudden 
overheating  (e.g.  Rummelsburg,  near  Berlin). 

123  Gms.  nitrobenzene  are  placed  in  a  sulphonating  pot  of  500  c.cs. 
capacity.  A  mixture  of  450  gms.  concentrated  sulphuric  acid  of 
66°  Be.  and  140  gms.  nitric  acid  of  47°  Be.  (sp.  gr.  1*48=88  %)  is 
allowed  to  drop  in  at  100°  during  half  an  hour,  with  very  efficient 
stirring,  which  is  best  effected  by  means  of  a  propeller  stirrer  or 
a  Witt's  bell-stirrer  which  must  dip  right  into  the  liquid.  The 
temperature  may  be  allowed  to  rise  to  115°,  and  the  addition  of  the 
acid  is  so  regulated  that  this  temperature  is  not  exceeded.  After 
all  has  been  added,  the  stirring  is  preferably  continued  for  a  further 
half-hour.  The  sulphonating  pot  is  covered  with  a  divided  sheet  of 
lead  so  as  to  prevent  the  escape  of  vapours.  The  nitration  is 
practically  quantitative. 

The  mixture  is  then  allowed  to  cool  to  about  70°,  and  is  poured 
into  half  a  litre  of  cold  water  with  good  stirring.  Some  nitrous 
fumes  are  evolved  (fume  cupboard),  and  the  crude  dinitrobenzene  is 


NITRATIONS  AND   REDUCTIONS  55 

at  once  precipitated  as  a  solid,  crumbly  mass.  The  waste  acid  is 
decanted  off  and  the  residue  melted  up  with  about  half  a  litre  of 
water.  After  cooling  and  pouring  off  the  washing  water,  the  operation 
is  repeated  with  the  addition  of  sufficient  soda  to  render  the  solution 
strongly  alkaline  to  litmus.  Finally,  the  dinitro  product  is  swirled 
round  at  80°  with  500  c.cs.  of  water,  to  which  10  c.cs.  of  30  %  soda  10  c.cs. 

"XT     /"\TT 

lye  have  been  added.  A  dinitro  product  is  obtained  in  this  way  ,  * o/\ 
which  has  a  solidifying  point  of  about  80°,  and  remains  practically 
uncoloured  with  soda  solution  ;  it  is  dried  in  a  drying  chest  at  90°, 
and,  on  cooling,  a  crystalline  cake  is  obtained  weighing  about  150  gms. 
Note  on  Works  Practice. — The  technical  product  is  not  usually 
quite  so  pure  as  it  contains  about  3  %  ^-dinitro-  and  i  %  o-dinitro- 
benzene  (see  also  under  ra-Phenylenediamine).  Dinitrobenzene  is 
an  extremely  poisonous  substance  and  quite  as  dangerous  as  prussic  acid. 
The  workmen  who  deal  with  it  must  always  change  their  clothes  in 
the  works  and  wear  gas  masks.  The  substance  can  even  penetrate 
through  the  skin  into  the  blood  and  causes  acute  Cyanosis,  a  form  of 
poisoning  in  which  the  lips  of  the  patient  become  blue,  the  pulse 
weakens,  and  frequently  death  supervenes  after  long  illness. 


Aniline  from  Nitrobenzene. 
Reaction :  NO2  NH2 


For  the  preparation  of  aniline  from  nitrobenzene  we  use  an 
autogenously  welded  iron  reaction  vessel,  such  as  is  shown  in  Fig.  4 
(p.  1 1).1     This  apparatus  is  provided  with  a  condenser  and  dropping 
funnel,  and  is  charged  with  200  gms.  iron  turnings,  300  c.cs.  water,   206  gms.  Fe. 
and  20  c.cs.  of  30  %  hydrochloric  acid.     The  mixture  is  boiled  up   H,°O!  " 
for  10  minutes  in  order  to  etch  the  iron.     123  Gms.  nitrobenzene   20  c.cs.  HC1. 
are  then  dropped  in  during  three-quarters  hour  at  the  boil,  with    *  mo1- 
very  vigorous  stirring,  taking  care  that  the  iron  is  kept  continuously   benzene  = 
swirled  up.     Considerable  heat  is  evolved,  and  the  nitrobenzene  is    I23  gms- 
reduced  to  aniline,  whilst  the  iron  becomes  oxidized  to   Fe3O4. 
Boiling  is  continued  under  the  reflux  until  the  distillate  which  runs 
back  down  the  condenser  is  colourless.     15  Gms.  soda  are  then  15 
added  to  the  reduction  liquid  and  the  aniline  driven^over  with  steam.   ora 
The  steam  is  led  in  through  the  neck  which  held  the  thermometer, 

1  A  similar  apparatus  may  be  used  with  advantage  for  sulphonating  by  means 
of  oleum,  as  it  is  unbreakable,  and,  therefore,  quite  free  from  any  possible  dangers 
which  might  attend  the  use  of  glass  or  porcelain  pots. 


56  INTERMEDIATE  PRODUCTS 

the  condenser  is  fitted  to  the  main  opening  by  means  of  a  bent  glass 
tube,  and  the  third  opening  is  closed  up. 

Aniline  is  soluble  in  water,  100  gins,  of  water  dissolving  about 
3  gms.  of  aniline.  For  this  reason  enough  salt  must  be  added  to 
the  aqueous  suspension  to  make  a  20  %  solution  of  salt,  in  which 
aniline  is  completely  insoluble.  After  standing  for  several  hours 
the  aniline  is  run  off  through  a  separating  funnel  and  distilled  over 
a  naked  flame.  The  first  portions  contain  traces  of  benzene  and  a 
little  water,  the  main  fraction  coming  over  at  182°  (99  %). 

The  yield  is  about  85  gms.  aniline  from  123  gms.  nitrobenzene. 

Notes  on  Works  Technique  and  Practice. — In  the  works  the 
aniline  is  distilled  over  by  means  of  steam  which  is  already  saturated 
with  aniline,  i.e.  the  boikr  is  fed  with  the  waste  water  from  the 
steam  distillation.  Weiler-ter-Meer,  however,  simply  extract  the 
aniline  water  with  nitrobenzene,  the  base  being  completely  removed 
from  the  liquid  by  this  means.  The  mixture  of  nitrobenzene  and 
aniline  is  then  reduced  directly  as  described  above.  By  this  means  it 
is  possible  to  avoid  the  use  of  boilers  charged  with  aniline  water  which 
always  cause  a  certain  amount  of  inconvenience.  Fig.  12  (Plate  V.) 
and  Fig.  1 1  (Plate  IV.)  show  the  type  of  apparatus  used  in  the  factory. 

On  the  large  scale  the  iron  is  added  gradually  and  less  water  is 
used.  The  yields  obtained  are  practically  quantitative,  about 
no  kgs.  pure  aniline  being  obtained  from  100  kgs.  benzene.  This  is 
distilled  in  vacuo  in  quantities  of  10,000-30,000  kgs.  The  heating 
is  always  effected  by  a  system  of  steam  pipes  fitted  inside  the  still. 

The  introduction  of  the  manufacture  of  aniline  gave  the  first 
impetus  to  the  development  of  the  colour  industry,  as  aniline  has 
always  been  one  of  its  most  important  products.  It  was  first  made 
in  England,  and  at  the  present  time  about  50-60  %  of  the  output 
is  utilized  for  the  production  of  Aniline  Black.  It  may  be  noted 
at  this  point  that  only  a  small  proportion  of  the  so-called  "  Aniline 
Dyes  "  are  actually  derivatives  of  aniline. 


Benzidine  from  Nitrobenzene. 

Reaction :  ^/O^^ 

N02  HNOH  N-       -N  N=    -N 

/\ 


\/  \/ 

Phenylhydroxyl-  Azoxybenzene.  Azobenzene. 


amine. 


NITRATIONS  AND   REDUCTIONS  57 

NH2 

/\ 
NH NH 


Hydrazobenzene . 

\ 

NH2  NH2 

Benzidine  Diphenyline. 

(ca.  85  %).  (ca.  15  %). 

Nitrobenzene  is  reduced  to  hydrazobenzene  by  means  of  cast- 
iron  borings  (in  strong  caustic  soda  solution),  which  must  have  the 
same  properties  as  the  iron  used  for  the  Bechamp-Brimmeyr  reduc- 
tion. It  is  very  important  to  remove  all  oil  from  the  turnings,  or 
else  too  much  will  get  into  the  benzidine.  Further,  the  iron  must 
be  very  finely  divided  as  only  the  surface  reacts.  By  the  use  of 
soda-lye,  water,  and  iron  turnings  it  is  possible  to  reduce  the  nitro- 
benzene step  by  step  and  to  obtain  quantitative  yields  of  hydrazo- 
benzene, though  the  last  stage  is  a  delicate  operation.  Consequently, 
a  modified  process  is  often  adopted  as  given  in  D.  R.  P.  138496  ; 
this  will  be  referred  to  later. 

The  actual  laboratory  apparatus  is  illustrated  on  Plate  XIV., 
Fig,  36.  Since  the  iron  turnings  offer  a  considerable  resistance  to 
stirring,  it  is  necessary  to  make  use  of  much  stronger  apparatus  than 
is  usual  in  the  laboratory.  It  will  be  found  convenient  to  use  a 
i  h.p.  water  turbine  or  electric  motor  which  can  be  made  to  turn 
a  number  of  driving  wheels.  On  the  small  scale  the  thermometer  is 
best  left  out,  owing  to  its  resistance,  measurement  of  the  temperature 
of  the  oil-bath  sufficing . 

123  Gms.  of  nitrobenzene  and  30  gms.  of  60  %  caustic  soda   ^23  gms, 
solution  are  first  placed  in  the  reduction  vessel  ;  the  mixture  is  then   Nitro- 
heated  to   125°  (oil-bath  at  about   140°).     A  reflux  condenser  is   30  gms.' 
provided,  as  a  certain  amount  of  water  distils  off  which  carries  away   S^/x 
some  nitrobenzene  and  reduction  products.     After  the  stirrer  has 
been  set  in  motion  400  gms.  of  very  finely  divided  iron  turnings  are   400  gms. 
added  during  half  an  hour,  which  have  been  previously  etched  by   Iro"  (°r  s°° 
means  of  80  gms.  of  60  %  soda- lye  at  120°.     (The  alkali  attacks  the   necessary), 
iron  with  evolution  of  hydrogen  which  contains  traces  of  strongly  jj  §jj ' 
smelling  phosphorus  compounds  ;    the  etched  iron  looks  like  so  (60  %). 
much  damp  sand,  and  on  exposing  to  the  atmosphere  readily  cakes 
together  to  solid  cement- like  lumps,  which,  on  a  large  scale,  may 
lead  to  considerable  difficulties.) 


INTERMEDIATE  PRODUCTS 


300  c.cs. 
Benzene. 


300  c.cs. 
Benzene. 
50  gms. 
NaOH 
(60  %). 

200  gms. 


The  reduction  starts  quickly  and,  after  all  the  iron  has  been 
added,  is  easily  completed  during  2-3  hours  at  125°.  Stirring  is 
continued,  and  the  mass  allowed  to  cool.  The  stirrer  must  on  no 
account  be  allowed  to  stop,  or  else  it  will  not  be  possible  to 
start  it  again.  When  the  temperature  has  reached  75°,  300  c.cs. 
benzene  are  added,  and  the  stirring  continued  for  5  minutes,  the 
apparatus  is  then  opened,  and  the  solution  of  azobenzene  poured 
out  into  a  distilling  flask.  There  should  be  practically  no  iron  in 
suspension  as,  with  the  concentration  of  caustic  soda  used,  emulsions 
are  rarely  formed.  The  extraction  is  repeated  three  times  at  75°, 
by  which  means  the  azobenzene  will  have  been  completely  removed. 
Care  must  be  taken  to  avoid  the  danger  of  fire. 

The  product  may  now  be  reduced  directly  to  hydrazobenzene, 
but  I  do  not  recommend  this  procedure,  as  inseparable  emulsions 
are  almost  always  formed,  i.e.  the  hydrazobenzene  cannot  be  sepa- 
rated from  the  iron  sludge.  If,  however,  it  is  desired  to  use  this 
method,  which  is  that  given  in  the  patent  referred  to,  then,  instead 
of  extracting,  300  c.cs.  of  benzene  are  added,  and  the  temperature 
kept  at  80°.  It  is  also  necessary  to  add  a  further  50  gms.  of  caustic 
soda-lye  (60  %),  otherwise  a  hard  cement  is  formed  by  degrees. 
To  obtain  complete  reduction  a  further  200  gms.  of  iron  turnings 
Fe*  are  added,  the  end  of  the  reaction  being  indicated  by  the  benzene 
solution  becoming  colourless.  The  separation  of  the  hydrazobenzene 
is  effected  as  with  the  azobenzene. 

The  azobenzene  is  obtained  completely  pure  on  distilling  off 
the  solvent,  but  before  doing  this  it  is  necessary  to  remove  all 
caustic  lye  by  means  of  carbon  dioxide  and  filtration.  The  yield  is 
practically  100  %  of  theory  or  about  90  gms. 


91  gms. 
Azobenzene. 
250  gms. 
Alcohol. 
200  gms. 
NaOH 
(30  %). 

220-250 
gms.  Zinc 
dust. 


IOO  C.CS. 

Alcohol 
(twice). 


Reduction  to  Hydrazobenzene. 

Reduction  by  means  of  Zinc  Dust. — 91  gms.  (=|  mol.)  azobenzene 
is  heated  up  with  250  gms.  alcohol  and  200  gms.  soda  lye  (30  % 
NaOH)  to  45°  in  an  iron  or  glass  vessel  provided  with  a  powerful 
stirrer  and  a  reflux  condenser.  Zinc  dust  is  then  added  by  degrees 
until  the  solution  is  only  a  faint  yellow.  According  to  the  purity  of 
the  zinc  dust,  about  200-250  gms.  will  be  required.  The  tempera- 
ture during  the  addition  must  not  be  allowed  to  exceed  60°,  otherwise 
aniline  is  readily  formed.  As  soon  as  the  liquid  has  been  bleached 
it  is  filtered  quickly  through  a  nutsch,  the  zinc  dust  made  into  a 
paste  with  100  c.cs.  90  %  alcohol,  quickly  boiled  up  and  filtered 
into  the  first  portion  ;  the  extraction  is  then  repeated.  The  zinc 


NITRATIONS  AND   REDUCTIONS 


59 


dust  is  spontaneously  inflammable,  and  must  not,  therefore,  be  thrown 
into  the  dustbin. 

The  aqueous- alcoholic  solution  separates  into  two  layers,  the 
upper  containing  the  hydrazobenzene,  and  the  lower  the  sodium 
zincate.  The  liquids  are  run  off  through  a  separating-funnel  and 
the  upper  is  saturated  with  carbon  dioxide  before  evaporating  off  . 
the  alcohol.  As  much  of  the  alcohol  as  possible  is  then  distilled 
off,  and  200  c.cs.  water  are  then  added  to  the  residue  with  shaking. 
The  hydrazobenzene  comes  out  first  of  all  as  an  oil,  which  then 
solidifies  to  coarse  crystalline  fragments.  After  filtering  off  it  is 
quite  pure  enough  for  further  working  up.  The  yield  of  dry  substance 
is  quantitative  =  92  gms. 

Modifications. — 91    gms.  of   pure    azobenzene    are  dissolved  in  91  gms. 
250  c.cs.  alcohol,  and  250  c.cs  of  20  %  ammonia  are  added.     A  ^z° ^e"szen 
rapid  stream  of  hydrogen  sulphide  is  passed  into  this  suspension,  Alcohol, 
which  heats  up  considerably,  becoming  darker  at  first,  and  then  250  c.cs. 
rapidly  colourless.      The  whole  reduction  occupies  about  f-i  hour.  2  '  0//0  NH3' 
On  cooling,  the  hydrazobenzene  separates  out  in  beautiful,  glistening, 
colourless  or  pale-yellow  crystals       After  standing   12  hours  the 
product  is  filtered  off  and  washed  with  a  little  water.     Yield  about 
92  gms. 

This  method  of  preparation  has  the  advantage  that  no  aniline 
is  produced  so  long  as  the  temperature  does  not  exceed  60°,  and  the 
hydrogen  sulphide  is  not  allowed  to  act  for  too  long. 


Conversion  of  the  Hydrazobenzene  to  Benzidine. 

Owing  to  the  easy  oxidizability  of  the  hydrazobenzene  it  should 
be  dealt  with  so  far  as  possible  in  the  moist  condition.     The  con- 
version must  be  effected  by  means  of  hydrochloric  acid  free  from 
sulphuric  acid  since  benzidine  sulphate  is  insoluble.1     The  finely 
divided  hydrazobenzene  is  added  cautiously  to  the  purified  acid, 
In  the  present  case  about  rz  mol.  technical  acid  (30  %  HC1)  is  -ca.  120  gms. 
used,  the  liquid  at  the  end  of  the  reaction  remaining  strongly  acid  HC1  (3°  0//o)t 
to  Congo.     The  temperature  of  the  transformation  is  kept  as  low 
as  possible  by  the  cautious  addition  of  100  gms.  of  ice.     The  hydrazo-    TOO  gms, 
benzene  may  be  added  quickly.     The  mass  is  then  stirred  con-   Tce' 
tinuously  for  5   hours,  and  is   heated   up   during  i   hour  to  80°, 
all   the   benzidine   and   diphenyline   going  into   solution.     At  this 

1  Hydrochloric  acid,  free  from  sulphuric  acid,  may  be  obtained  by  mixing 
*5  %  commercial  acid  with  barium  chloride  solution,  until  no  further  precipitate 
is  formed. 


60  INTERMEDIATE  PRODUCTS 

stage  of  the  operations  oily  drops  of  azobenzene  frequently  form, 
but  only  if  the  temperature  has  been  too  high  or  if  much  oxidized 
hydrazobenzene  has  been  used. 

The  product  is  now  allowed  to  cool  until  the  precipitate  becomes 
easily  filterable,  which  is  usually  at  about  60°.  Where  the  reduction 
.  has  been  effected  by  means  of  ammonium  sulphide  a  fairly  heavy 
precipitate  of  sulphur  is  formed  which  is  filtered  off  warm.  The 
residue  is  washed  out  with  50  c.cs.  of  water  at  60°.  The  solution 
of  the  benzidine  is  always  coloured  blue-  to  red- violet.  The 
resultant  benzidine  hydrochloride  is  now  precipitated  with  the 
calculated  quantity  of  sulphuric  acid  or  bisulphate  (the  cheapest 

55  gms.  form  of  sulphuric  acid).     For  this  purpose  about  55  gms.  of  66°  Be. 

<to°SBe4'  sulphuric  acid  are  required.     The  benzidine  sulphate  is  precipitated 

instantaneously  as  a  thick,  crystalline  deposit.  It  may  therefore 
be  filtered  off  after  a  few  minutes  and  thoroughly  washed  with 
water  containing  J  %  sulphuric  acid.  It  is  then  stirred  up  afresh 

50  gms.  with  400  c.cs.  of  water  and  made  alkaline  with  about  50  gms.  soda. 

Na2CO3.  The  decomposition  of  the  sulphate  must  be  effected  as  quickly  as 
possible,  as  it  has  been  found  that  after  a  few  hours  the  salt  does  not 
react  so  rapidly  with  soda.  The  benzidine  sulphate  mother-liquor 
is  deeply  coloured,  and  gives  a  precipitate  of  about  8  gms.  diphenyline 
on  making  alkaline  with  soda.  The  free  benzidine  base,  which 
always  becomes  a  little  darker  on  standing,  separates  out  as  a  grey- 
white  flocculent  mass  ;  it  is  filtered  off  and  well  washed  with  a 
little  cold  water.  The  dried  product  has  an  apparent  purity  of 
98  %,  but  on  distillation  about  5  %  of  the  total  weight  always 
remains  behind  in  the  form  of  pitch.  With  very  exact  working, 
which  is  by  no  means  easy  to  carry  out,  a  yield  is  obtained  from 
i  gm. -molecule  of  nitrobenzene  of  about  80  gms.  purest  distilled  benzidine 
base  (B.p.  405°  ;  24O°/i5  mm.). 

Notes  on  Works  Technique  and  Practice. — The  manufacture  of 
benzidine  has  developed  into  one  of  the  most  important  operations 
in  colour  technology,  as  the  direct  cotton  colours  obtained  from  it 
are  literally  indispensable.  The  price  of  the  product  before  the 
war  was  very  low,  owing  to  the  keen  competition  of  the  different 
factories,  namely  about  2  fr.  90  per  kilo.  Whilst  the  reduction 
of  nitrobenzene  was  carried  out  as  recently  as  15  years  ago  exclusively 
with  caustic  soda-lye,  methyl  alcohol,  and  zinc  dust,  the  situation 
has  altered  completely  at  the  present  time,  as  there  are  now  only 
two  processes  which  can  compete.  The  one  which  we  have  dis- 
cussed replaces  these  expensive  reducing  agents  by  the  cheaper 
iron,  which  is  recovered  as  iron  oxide  and  can  then  go  back  to  the 


NITRATIONS  AND   REDUCTIONS  61 

• 

blast-furnace.  For  the  last  stage  of  the  reduction  zinc  dust  is  often 
made  use  of  in  place  of  iron,  but  in  the  works  it  is  more  advantageous 
to  complete  this  stage  also  by  means  of  iron  powder.  Once  the 
azobenzene  has  been  isolated,  the  chief  difficulties  disappear,  as  the 
main  bulk  of  the  iron  sludge  has  been  got  rid  of.  The  reduction 
of  the  azobenzene  with  hydrogen  sulphide,  however,  is  also  worth 
consideration  as,  in  certain  factories,  this  is  a  cheap  by-product ; 
it  is  impossible  to  say  beforehand  which  process  is  to  be  preferred. 
The  quality  of  the  iron  must  be  the  same  as  that  used  for  the  Bechamp 
reduction,  and,  further,  the  borings  must  be  carefully  freed  from 
grease. 

The  apparatus  used  on  the  works  must  be  built  very  strongly 
as  the  stiff  iron  mass  offers  very  great  resistance  to  stirring. 
Plate  XL,  Fig.  29,  illustrates  a  reaction  vessel  of  this  type  with 
duplex  stirring  gear.  In  this  case  the  stirrer,  however,  is  made 
somewhat  differently,  like  a  plough,  in  order  that  the  paddles  may 
go  through  the  iron  sludge  more  easily. 

The  extraction  may  be  carried  out  in  the  reduction  vessel  itself, 
the  benzene  solution  being  run  off  through  side  outlets.  Special 
extraction  apparatuses  are  made  also,  in  which  the  iron,  after 
separating  from  the  reduction  liquor,  is  extracted.  Tip-up 
vessels,  which  can  be  quickly  and  easily  emptied,  are  some- 
times employed.  Apparatus  of  this  type  is  very  heavy,  but  has 
the  advantage  over  those  which  are  emptied  through  a  bottom 
exit-tube  that  it  has  no  spiral  conveyor  which  easily  gets 
stopped  up. 

Increasing  use  is  being  made  of  centrifuges  for  separating  the 
mother- liquors  from  the  precipitates,  with  the  exception  of  the 
filtration  of  the  benzidine  sulphate,  which  is  frequently  performed  by 
means  of  a  nutsch  (Fig.  VI.)  or  a  filter-press.  So  far  no  use  has 
been  found  for  the  diphenyline  obtained  as  a  by-product.  Although 
the  5  %  loss  on  distillation  has  deterred  most  factories  from  isolating 
the  benzidine  in  this  way,  I  am  quite  certain,  from  my  own  experience, 
that  this  loss  is  apparent  rather  than  real. 

The  superiority  of  the  distilled  benzidine  shows  itself  particularly 
in  the  manufacture  of  complex  triazo  colours,  as  in  these  cases  the 
increased  price  is  more  than  made  up  for  by  the  better  yields. 
Colours  such  as  Direct  Deep  Black  E.W.  (q.v.)  or  Dianil  Brown 
3GN,  when  prepared  from  quite  pure  components,  will  always  excel 
those  obtained  from  less  pure  materials.  It  is  perhaps  hardly 
necessary  to  remark  that  all  by-products,  such  as  caustic-lye,  unused 
iron,  and  solvent  should  be  most  carefully  recovered. 


INTERMEDIATE  PRODUCTS 


NH2 

-N2-/     \S03H 


Benzidine. 


\___X 

Sulphanilic  acid. 
m-Phenyline  diamine. 

DIANIL  BROWN   3GN. 

Finally,  I  may  mention  that  the  second  process,  the  electrolytic, 
will,  in  my  opinion,  gradually  displace  even  the  Weiler-ter-Meer 
process,  in  spite  of  all  difficulties.  It  has  a  great  superiority  in  that 
absolutely  no  metal  is  required,  which  was  a  great  advantage  during 
the  war,  when  it  was  extremely  difficult  to  obtain  cheap  zinc 
dust.  At  the  present  time  there  is  only  one  factory,  and  that  in 
Switzerland,  which  carries  out  this  process  successfully. 


2:2'-Benzidine  Disulphonic  Acid  from  Nitrobenzene. 

Reaction  : 

NO2  NO2  HNOH 

/\  /\ 

I       I 

JSO.H 


Phenylhydroxylamine 
sulphonic  acid. 


N N 

and 


Azobenzene  disulphonic  acid. 

NH2 NH2 

/\        S\  •*      H03S 

HOgSl^/l        k^SOaH 

NH2         NH2 

Hydrazobenzene-disulphonic  acid.  2  : 2' '-Benzidine  disulphonic  acid. 

ft 


gs 


Ms  as 


PLATE   VI, 


NITRATIONS  AND   REDUCTIONS  63 

The  preparation  of  nitrobenzene  sulphonic  acid  has  been  fully 
described  in  connection  with  metanilic  acid.  The  reduction  process 
differs  only  from  similar  reactions  in  that  it  is  carried  out  purposely 
in  dilute  aqueous  solution  in  the  present  case,  and  in  three  stages. 
It  is  possible  to  obtain  benzidine  disulphonic  acid  with  the  use  of  a 
minimum  quantity  of  caustic  soda  and  zinc  dust. 

If  the  sodium  salt  used  is  not  quite  pure,  the  press-cakes  of 
sodium  nitrobenzene  sulphonate  corresponding  to  100  gms.  nitro-   ioo  gms. 
benzene  are  dissolved  in  about  30  gms.  soda  so  that  the  solution  is  ^^^j. 
exactly  neutral  to  litmus  ;    it  is  then  made  up  to  ij  litres  at  10°,  phonic  acid. 
10  gms.  of  ammonium  chloride  are  added,  and  the  liquid  vigorously  NH°ci°S 
stirred  by  means  of  a  propeller  stirrer.     120  Gms.  zinc  dust  are  then  I20  gms 
added  during  2  minutes,  a  teaspoonful  at  a  time  ;     finely  crushed  Zinc  dust. 
ice  is  also  added  from  time  to  time  to  keep  the  temperature  below 
20°,  stirring  being  continued  for  20  minutes.    120  Gms.  30  %  caustic  i2o  gms. 
soda-lye  are  poured  in  quickly,  and  the  mass  warmed  up  to  70°  J^i/l 
without  stirring.     The  solution,  which  was  originally  colourless,  at 
once  becomes  orange-yellow  owing  to  the  formation  of  the  azo-  and 
azoxy-benzene  sulphonic  acids,  and  is  allowed  to  stand  for  at  least 
3  hours  or,  better,  over-night. 

Next  day  the  product  is  neutralized  cautiously  by  the  addition 
of  about  90  gms.  concentrated  hydrochloric  acid,  drop"  by  drop,  Ca.  90  gms. 
until  no  reaction  is  given  with   thiazole  paper.      After  the  liquid  conc>  HCL 
has  been  heated  up  to  80°  a  further  40  gms.  zinc  dust  are  added.  40  gms. 
If  the  colour  has  not  disappeared  after  5  minutes,  a  further  quantity  Zmc  dust- 
of  hydrochloric  acid  is  dropped  in  slowly  at  75-80°.     The  change 
of  colour  from  a  dirty  brown  to  a  clear  light  grey  takes  place  in  less 
than  5  seconds  as  soon  as  the  neutral  point  has  been  reached.     The 
liquid  now  contains  the  hydrazine  sulphonic  acid,  its  volume  being 
about  1*8  litres,  and  is  quickly  run  through  a  filter  to  prevent  further 
reduction  to  metanilic  acid,  the  zinc  dust  being  well  washed  out. 
After  cooling,  the  filtrate  is  treated  at  20°  with  120  c.cs.  cone,  hydro-   120  c.cs. 
chloric  acid.     In  a  few  minutes  a  glistening  precipitate  forms,  con  -  conc>  HC  ' 
sisting  of    colourless  hard  crystals  of    2:2'-benzidine  disulphonic 
acid,  the  liquor  becoming  yellow  through  autoxidation  ;  a  few  drops 
of  stannous  chloride  solution  are  therefore  added  to  decolourize  it. 
Although  the  benzidine  disulphonic  acid    is  extremely  sparingly 
soluble  in  water  (less  than  i  gm.  per  litre),  it  separates  out  very 
slowly,  so  that  the  product  must  be  allowed  to  stand  for  a  couple 
of  days  before  filtering  and  washing  with  cold  water. 
yield  about  65  gms. 

Notes  on  Works  Technique  and   Practice. — On  the  large  scale, 


64 


INTERMEDIATE  PRODUCTS 


Sulphanilic 
acid. 


35  gms. 
H2S04. 

zi  gms. 
NaN02. 


130  gms. 
NaHSOj 
solution. 

25-40  gms. 
NaOH 
(35  %)• 


where  one  has  to  deal  with  volumes  of  4000  to  5000  litres,  the 
crystallization  of  the  2:2'-benzidine  disulphonic  acid  occupies  at 
least  3  days.  In  order  to  secure  as  rapid  cooling  as  possible  a  leaden 
coil,  through  which  cold  water  is  circulated,  is  placed  in  the  wooden 
tub. 

Owing  to  its  insolubility  the  sulphonic  acid  must  be  diazotized 
indirectly  ;  it  is  dissolved  in  the  requisite  amount  of  water  and 
soda,  the  neutral  solution  mixed  with  sodium  nitrite,  and  the  mixture 
allowed  to  run  in  a  thin  stream  into  hydrochloric  or  sulphuric  acid. 


Phenylhydrazine  Sulphonic  Acid  from  Sulphanilic  Acid. 
Reaction  : 


NH, 


S0H 


\y 

S03J 


N2.SO3H        NH.NH.S03H       NH.NH2 

1s 


I 

SOoH 


S03H 


SOoH 


3/1  o  Gm. -molecule  technical  sulphanilic  acid  (100  %)  is  dissolved 
in  200  c.cs.  water  with  the  aid  of  16  gms.  of  soda,  the  residual  aniline 
being  boiled  off  with  steam.  The  filtered  solution  is  cooled  down 
in  a  glass  vessel,  35  gms.  cone,  sulphuric  acid  are  added,  and  the 
whole  cooled  further  to  12°  (external  cooling)  ;  it  is  then  treated 
with  a  solution  of  21  gms.  100  %  sodium  nitrite  in  50  c.cs.  water 
(3/10  gm.-molecule)  during  half  an  hour,  with  continuous  stirring, 
until  a  distinct  and  permanent  reaction  is  given  with  nitrite  paper. 
The  diazosulphanilic  acid  comes  out  as  fine  crystals,  which  are 
filtered  off  at  12-14°  on  a  small  suction  filter.  The  residue  of 
crystals  are  rinsed  out  of  the  beaker  by  means  of  the  mother- liquor.1 

The  diazo  compound  so  produced  is  added  to  a  mixture  of  130 
gms.  sodium  bisulphite  solution  (containing  25  %  SO2),  and  just 
enough  35  %  caustic  soda  solution  to  cause  the  sulphite  to  give  a 
distinct  reaction  with  phenolphthalein  paper  ;  according  to  the 
quality  of  the  technical  bisulphite  25-45  gms-  soda-lye  will  be 
required.  If  too  little  be  used  the  hydrazine  sulphonic  acid  becomes 
discoloured  later  on  and  deposits  resinous  matter.  [The  use  of 
solid  commercial  sodium  sulphite  is  unsatisfactory,  as  its  SO2  content 
is  too  variable.]  The  temperature  of  the  mixture  is  kept  below  50° 
by  placing  the  vessel  in  ice  water  and  stirring  well.  The  diazo 

1  The  moist  diazosulphanilic  acid  is  quite  harmless,  but  it  is  highly  explosive 
in  the  dry  state,  so  that  great  care  must  be  taken, 


NITRATIONS   AND   REDUCTIONS  65 

sulphanilic  acid  is  at  once  converted  into  the  sulphophenyl-azo- 
sulphonic  acid,  which  is  allowed  to  stand  for  an  hour. 

It  may  be  converted  into  the  hydrazine  sulphonic  acid  in  various 
ways.  The  simplest  is  the  following,  which  is  also  that  used 
technically.  The  yellow  solution  of  the  azo-sulphonic  acid  is 
heated  to  boiling  in  a  porcelain  dish,  and  the  boiling  solution  treated 
with  30  %  hydrochloric  acid  (250  gms.)  until  the  reaction  is  very  ca.  250  gms. 
strongly  mineral  acid.  This  operation  should  take  about  half  an  3°  %  HC1' 
hour,  in  order  to  allow  the  sulphurous  acid  set  free  from  the  neutral 
sulphite  sufficient  time  to  exert  its  reducing  action  (fume  cupboard  !). 
If  the  solution  should  not  by  then  have  become  decolorized  a  little 
more  zinc  dust  may  be  carefully  added.  The  phenylhydrazine 
sulphonic  acid  crystallizes  out  on  cooling  and,  after  standing  12 
hours,  is  filtered  off  and  washed  with  a  little  water.  Yield  about 
50  gms.  100  %  product. 

The  quantitative  estimation  is  carried  out  by  condensing  a 
moderate  amount  of  the  substance  with  aceto-acetic  ester  in  acetic 
acid  solution  and  weighing  the  resultant  pyrazolone. 

Notes  on  Works  Technique  and  Practice. — The  preparation  of 
aryl-hydrazine  sulphonic  acids  has  recently  gained  considerably  in 
importance,  as  they  are  the  starting-points  for  various  yellow  and 
red  colouring  matters  which  are  fast  to  light,  certain  of  which  are 
mentioned  later.  Most  amines  of  the  benzene  series  may  be 
similarly  converted  into  the  corresponding  hydrazines  ;  the  chlor- 
phenyl-hydrazine  sulphonic  acids  and  the  tolyl-hydrazine  sulphonic 
acids,  for  instance,  are  largely  manufactured.  Certain  of  them  are 
somewhat  difficult  to  reduce  completely,  so  that  the  elimination  of 
the  sulphonic  group  attached  to  the  nitrogen  atom  only  takes  place 
at  110-135°.  Such  sulphonic  acids,  therefore,  are  either  brought 
to  the  necessary  temperature  in  lead-lined  autoclaves,  or  else  the 
difficulty  is  got  over  by  the  following  neat  device  :  sulphuric  acid  is 
used  in  place  of  hydrochloric  acid  for  setting  free  the  sulphurous 
acid,  and  is  allowed  to  run  under  the  surface  of  the  boiling  liquid. 
The  reaction  liquid  thereby  heats  up  very  strongly  and  the  sulphuric 
acid  hydrolyses  the  sulphohydrazine  sulphonic  acid  without  diffi- 
culty ;  very  occasionally  it  is  necessary  to  add  a  little  stannous 
chloride  or  zinc  dust.  On  the  large  scale,  with  \  kg.-molecule 
charges,  the  hydrolysis  and  reduction  occupy  about  3  hours.  The 
yields  are  up  to  95  %,  and  the  crystallizations,  as  in  the  case  of 
benzidine  disulphonic  acid,  occupy  several  days. 


66  INTERMEDIATE  PRODUCTS 

w-Nitraniline  from  m-Dinitro-benzene. 
Reaction  : 

N02  N02 


500  C.cs.  of  water  are  heated  to  85°  in  an  iron  or  glass  beaker 
ioo  gms.         of  i  J   litres   capacity,   100  gms.  dinitro-benzene  are  then  added, 

Dinitro-          an(j  by  means  of  very  efficient  stirring  are  practically  emulsified 
benzene.  *,  J  .  ,         r 

(propeller  stirrer  ;  caution  required  owing  to  the  highly  poisonous 
245  gms  vapours).  245  Gms.  of  crystallized  sodium  sulphide  (Na2S+9  aq.) 
+9H2O  dissolved  in  200  c.cs.  of  water  are  then  allowed  to  run  into  this 
emulsion  from  a  dropping  funnel  during  10  minutes.  The  dinitro- 
benzene  is  partially  reduced  by  alkali  sulphide,  w-nitraniline  being 
formed.  The  end-point  of  the  reaction  may  be  recognized  by  the 
fact  that  a  drop  of  the  solution  on  a  filter  paper  gives  a  black 
streak  of  metallic  sulphide  with  an  iron  or  copper  sulphate  solution. 
As  soon  as  the  blackening  remains  for  20  seconds,  the  mixture  is 
500  gms  cooled  at  once  to  20°  by  throwing  in  500  gms.  of  ice,  and,  after 
standing  for  several  hours  the  w-nitraniline  is  filtered  off  ;  it  may  be 
recrystallized  from  boiling  water,  but  for  most  purposes  this  is 
unnecessary.  For  works  use  the  crude  product  is  simply  dissolved 
in  hydrochloric  acid,  the  sulphur  filtered  off,  and  the  solution 
utilized  directly.  The  yield  is  about  55  gms.  pure  recrystallized 
n\-nitr  aniline. 

A  solution  of  sulphur  and  sodium  sulphide  has  also  been  recom- 
mended for  the  reduction,  but  this  process  is  not  advised,  as  it  leads 
to  poorer  yields  and  less  pure  products. 

It  may  be  noted  here  that  certain  nitro  compounds  cannot  be 
partially  reduced  in  this  simple  manner,  as  the  reduction  for  the  most 
part  goes  too  far  ;  for  further  details,  see  the  reduction  of  picric 
acid  to  picramic  acid  (p.  77). 

Other  nitro  compounds  must  be  reduced  in  ammoniacal  solution 
with  exactly  the  calculated  quantity  of  hydrogen  sulphide.  It 
happens  frequently  that  mere  careful  weighing  of  the  hydrogen 
sulphide  is  insufficient,  so  that  it  is  necessary  to  make  use  of  various 
devices.  Thus  dinitro-phenol  can  only  be  satisfactorily  reduced 
to  nitro-amino-phenol  if  it  is  used  in  the  form  of  its  very  finely 
divided  sodium  salt,  as  obtained  directly  by  the  hydrolysis  of  dinitro- 
chlor-benzene  (see  Sulphur  Black  T),  which  is  reduced  in  ammoniacal 
solution  at  about  60°  with  exactly  the  calculated  quantity  of  hydrogen 


NITRATIONS  AND   REDUCTIONS  67 

sulphide.     The  nitro-amino-phenol  so   obtained  is  then  best  re- 
crystallized  from  boiling  water. 

The  combination  of  the  sparingly  soluble  diazo  compound  with 
the  m-phenylene-diamine  sulphonic  acid,  described  on  p.  46, 
affords  the  cheapest  chrome-brown  on  the  market.  The  coupling 
is  effected  in  a  completely  neutral  solution,  and  as  concentrated 
as  possible,  at  28°  during  2-3  days. 
,  Chrome  Brown  R  (Kalle)  : 

OH  NH2 


SO3H 


w-Phenylene-diamine  from  w-Dinitro-benzene. 
Reaction :  NO2  NH2 


For  the  preparation  of  /w-phenylene-diamine  the  H-acid  apparatus 
shown  in  Fig.  5  is  made  use  of,  and  is  charged  with  168  gms. 
w- dinitro-benzene.  As  the  commercial  w-dinitro-benzene  is  not  benzene 
pure  it  is  never  possible  to  obtain  yields  higher  than  90  %  of  theory. 
Commercial  dinitro-benzene  has  a  melting-point  of  about  80°,  and 
always  contains  varying  percentages  of  isomeric  products,  together, 
usually,  with  some  dinitrophenol  which  is  easily  recognized  by  the 
more  or  less  intense  yellow  colour  which  it  gives  on  boiling  with 
soda  or  with  caustic  soda-lye. 

1 1  Litres  of  water  and  300  gms.  fine  iron  turnings  are  placed  in  ^°0  gms 
the  reduction  vessel ;   the  iron  is  etched  with  20  c.cs.  cone,  hydro-  20  c  cs 
chloric  acid,  and  the  mixture  heated  to  boiling  for  at  least  5  minutes.  (30  %)• 
The  dinitro-benzene  is  then  added  in  small  portions  of  not  more 
than  2  gms.  at  a  time  with  continuous  stirring.     It  will  be  noticed 
that  the  liquid  first  becomes  yellow,  due  to  the  formation  of  m- 
nitraniline  ;   it  froths  up  on  each  addition,  sometimes  so  vigorously 
that  it  becomes  necessary  to  spray  water  on  to  the  surface.     For  the 
reduction  to  go  properly  the  temperature  must  always  be  kept  up 
to  the  boiling-point.     After  every  second  addition  of  dinitro-benzene 
it  is  necessary  to  wait  until  a  drop  on  filter  paper  is  colourless. 
If  the  process  be  hurried  too  much  the  liquid  becomes  brown,  due 
to  the  formation  of  azoxy  compounds.     These  prevent  the  progress 
of  the  reduction,  which  must  then  be  regarded  as  a  failure,  and  must 


68  INTERMEDIATE  PRODUCTS 

be  stopped.  This  phenomenon  is  one  of  the  most  undesirable  which 
takes  place  in  any  reduction  process.  It  occurs  also  if  poor  quality 
iron  be  used,  for  which  reason  it  is  most  necessary  before  purchase 
always  to  test  the  samples  of  iron  very  carefully  as  to  their  activity. 
With  a  little  practice,  however,  it  is  easy  to  reduce  the  dinitro-benzene 
satisfactorily  in  40  minutes.  At  the  end  a  solution  is  obtained  which 
is  frequently  either  colourless  or  pale  brown  and  darkens  on  keeping  ; 
it  is  then  boiled  for  at  least  5  minutes,  the  water  which  evaporates 
being  replaced  so  as  to  keep  the  volume  at  about  2  litres,  corresponding 
to  a  content  of  about  45  gms.  diamine  per  litre. 

The  boiling  solution  is  now  treated  very  carefully  with  solid 
ca.  10  gms.  calcined  soda  in  small  portions  (about  10  gms.).  As  soon  as  the 
Na2CO3.  reaction  with  litmus  is  distinct  the  product  is  boiled  for  a  further 
5  minutes,  in  order  to  decompose  completely  the  soluble  iron  com- 
pound of  any  hydroxylamine  which  may  be  present.  The  liquid 
should  not  be  filtered  until  a  test  on  filter  paper  gives  no  black  stain 
with  sodium  sulphide  solution  (i-io);  This  test  should  never  be 
omitted  on  the  large  scale,  and  is  likely  to  save  much  annoyance.1 
The  liquid  is  then  filtered  into  a  bolt-head  which  has  been  previously 
warmed,  and  the  clear  filtrate  is  treated  with  sufficient  hydro- 
chloric acid  to  cause  a  slight  acid  reaction  to  litmus.  A  solution  of 
ra-phenylene- diamine  obtained  in  this  manner  keeps  well.  Yield 
about  95  gms.,  100  %.  The  quantitative  estimation^  carried  out 
in  very  dilute  solution  at  o°  with  diazotized  aniline,  as  in  the  case 
of  H-acid,  except  that  it  is  unnecessary  to  add  soda. 

This  technical  solution  suffices  for  many  purposes,  but  a  purer 
diamine  is  preferable  as  the  final  yields  are  thereby  improved.  For 
this  purpose  the  aqueous  solution  is  evaporated  first  over  a  naked 
flame,  and  then  preferably  in  vacuo,  until  it  contains  about  40  %  of 
base  ;  it  may  now  be  distilled  in  vacuo  or,  more  simply,  it  can  be 
frozen  out  at  o°.  In  order  to  start  the  crystallization  with  this  "  cold  " 
process  it  is  necessary  to  "  seed  "  the  solution  with  a  crystal  of  pheny- 
lenediamine.  The  purified  diamine  forms  beautiful  white  prisms  con- 
taining half  a  molecule  of  water,  and  differs  from  the  impure  product 
in  being  perfectly  stable  ;  o-  and  />-diamines  are  present  in  the 
aqueous  mother-liquor  in  concentrated  form,  which  is  the  reason 
why  the  commercial  liquor  is  so  easily  oxidizable.  Orthodiamine 
gives  immediately  the  characteristic  blue-black  coloration  with 
aniline,  acetic  acid,  and  a  little  bichromate,  by  means  of  which  it 
can  be  readily  identified  in  the  solution. 

1  If  in  spite  of  long  boiling  the  iron  reaction  persists,  the  iron  may  be  precipi- 
tated with  a  little  ammonium' sulphide. 


NITRATIONS  AND   REDUCTIONS  69 

The  English  firm  of  Read,Holliday  &  Sons  l  places  a  m-phenylene- 
diamine  on  the  market,  which  has  been  recrystallized  from  water, 
and  in  spite  of  its  somewhat  higher  price,  it  is  strongly  to  be  recom- 
mended owing  to  the  excellent  yields  of  colour  obtained  by  its  use. 

The  homologous  i:2:4-toluylene-diamine  is  obtained  in  a 
precisely  similar  manner  to  m-phenylene-diamine.  It  is  characterized 
by  its  great  purity  even  in  its  aqueous  solution,  as  the  technical 
dinitro- toluene  is  almost  chemically  pure  ;  in  spite  of  this,  however, 
it  is  usually  evaporated  down  and  recrystallized  in  order  to  obtain 
a  100  %  product.  Dinitrochlorbenzene,  ^-nitraniline,  and  other 
insoluble  nitro  compounds  behave  in  a  similar  manner. 

The  exceptions,  however,  are  all  those  compounds  containing 
carboxyl  groups  (COOH).  These  cannot  be  reduced  with  iron  in 
neutral  solution,  or  only  if  special  precautions  be  taken,  as  insoluble 
iron  compounds  are  immediately  formed.  For  instance,  the  im- 
portant nitro-salicylic  acid  must  be  reduced  by  means  of  tin  and 
hydrochloric  acid,  the  tin  being  recovered  without  loss  by  precipita- 
tion with  zinc  dust.  Chlornitro-benzoic  acid  is  best  reduced  in 
neutral  solution  with  zinc  dust.  Nitrophenol  sulphonic  acids,  etc., 
however,  are  reduced  by  means  of  sodium  sulphide  (or  hydro- 
sulphide)  solution  under  pressure  at  120-150°. 


^-Nitraniline  and  ^-Amino-acetanilide  from  Aniline,2 

Reaction  : 

NH2  NH(COCH3)   NH(COCH3)  NH(COCH3) 

+     a  little     f>°2 

x/ 

N02 

Aniline.  Acetanilide.        Nitro-acetanilide. 

NH2  NH(COCH3) 

->         ,/\  /\ 

hydrolysis     I          I     or  reduction     |          | 

N02  NH2 

p  -Nitr aniline .  p  -Amino-acetanilide . 


1  This   firm  is  now  absorbed  in  the   British  Dyestuffs  Corporation,  Ltd. — 
F.  A.  M. 

2  See  also,  P.  Miiller,  Ch.  Z.  1912,  1049,  1055. 


INTERMEDIATE  PRODUCTS 


1 86  gms. 
Aniline. 
1 68  gms. 
Glacial 
acetic  acid. 


50  c.cs. 
Glacial 
acetic  acid. 


200  gms. 
Acetanilide. 
800  gms. 
H2S04, 
66°  Be. 


154  gms. 
HN03 
(60  %). 
150  gms. 
H2S04, 
66°  B6. 


500  gms. 
Water. 
500  gms. 
Ice. 


Acetanilide. 

1 86  Gms.  of  purest  aniline  are  heated  with  the  same  volume 
of  100  %  (glacial)  acetic  acid  in  a  bolthead  of  J  litre  capacity.  Highly 
concentrated  acetic  acid  has  a  strong  action  on  most  metals,  for  which 
reason  it  is  necessary  to  work  in  glass  vessels  in  the  laboratory. 
The  temperature  is  kept  at  130°  for  ten  hours,  using  a  reflux  con- 
denser, after  which  about  25  c.cs.  water  and  acetic  acid  are  distilled 
off  through  a  Liebig  condenser  and  then  a  further  50  c.cs.  of  glacial 
acetic  acid  are  added.  During  the  second  day  sufficient  water  and 
acetic  acid  are  distilled  off  for  the  temperature  of  the  melt  to  rise 
to  240°.  A  further  70  gms.  of  acetic  acid  distil  over,  the  strength 
of  the  last  fraction  being  over  80  % .  The  acetylation  is  now  practi- 
cally quantitative.  The  acetanilide  is  poured  into  a  copper  tray 
and  the  hard  melt  finely  powdered.  Yield  about  270  gms.  acetanilide. 

A  still  purer  product  is  obtained  by  stirring  the  powdered  melt 
with  a  little  water  at  70°,  after  which  it  is  cooled  down,  filtered  off, 
washed  and  dried.  In  this  way  the  last  traces  of  acetic  acid  are 
removed.  The  acetanilide  so  obtained  has  a  melting-point  of 


IIO-III 


Nitro-acetanilide . 


200  Gms.  of  dry, finely  powdered  acetanilide  are  added  to  800  gms. 
concentrated  sulphuric  acid  of  66°  Be.,  using  the  apparatus  described 
on  p.  5.  The  temperature  should  not  rise  above  25°,  as  hydrolysis 
otherwise  occurs.  The  acetanilide  dissolves  completely  to  a  clear 
solution  in  the  course  of  an  hour  or  two.  The  liquid  is  now  well 
cooled,  and  a  mixture  of  154  gms.  nitric  acid  of  60  %  (40°  Be.)  and 
150  gms.  of  92  %  sulphuric  acid  are  added  during  about  one  hour. 
The  nitrating  temperature  should  not  exceed  2-3°,  or  else  rather 
much  orthonitro  compound  is  formed.  When  all  has  been  added 
stirring  is  continued  for  at  least  a  further  three  hours,  the  liquid 
being  preferably  allowed  to  stand  all  night.  A  test  portion  of  the 
mixture  on  pouring  into  water  and  boiling  with  soda  lye  should 
give  no  odour  of  aniline. 

The  product  is  now  poured,  with  good  stirring,  on  to  500  gms. 
of  water  and  500  gms.  of  ice.  The  nitro-acetanilide  is  at  once 
precipitated,  and  may  be  filtered  off  after  an  hour  without  loss. 
With  proper  working  the  theoretical  quantity  of  nitric  acid  will 
suffice  as  is  often  the  case  in  colour  technology.  No  harm,  however, 
results  from  a  slight  excess,  as  a  second  nitro  group  can  only  be 


NITRATIONS  AND   REDUCTIONS  71 

introduced  into  the  molecule  with  difficulty.  The  nitro-acetanilide 
left  on  the  filter  is  now  thoroughly  washed  with  water,  then  stirred 
up  with  a  litre  of  water,  sufficient  soda  added  to  give  a  distinct  blue 
colour  to  litmus  paper,  and  boiled.  As  a  result  of  this  treatment 
only  the  o-nitro-acetanilide  is  hydrolysed.  The  product  is  filtered 
at  50°  and  well  washed  out  with  water.  The  yield  so  obtained  is 
about  90  %  of  theory. 

The  hydrolysis  of  the  acetyl  derivative  is  always  carried  out  Nitro-acet- 
with  soda  lye  ;  the  moist  press-cakes  of  nitro-acetanilide  are  stirred  *™ohde  f™ 
up  with  an  equal  weight  of  water  and  the  suspension  then  boiled  Acetanilide 
with  200  gms.  of   35   %   soda  lye.     The   reaction   must    remain  200gms. 
distinctly  alkaline.    After  about  three  hours  a  test  portion  should 
give  a  clear  solution  in  hydrochloric  acid,  thus  indicating  complete 
saponification.     The  liquor  is  then  cooled  to  40°  and  filtered.     The 
product  is  carefully  washed  with  cold  water  and  is  then  chemically 
pure.     Yield  about  100  gms.  nitr aniline  from  93  gms.  aniline. 


Amino-acetanilide  from  Nitro-acetanilide. 

This  azo  component  is  prepared  by  the  neutral  reduction  of 
nitro-acetanilde  in  practically  the  same  way  as  has  already  been 
described  several  times.     In  an  iron  beaker  provided  with  a  pro- 
peller stirrer  are  placed  250  gms.  cast-iron  borings,  15  c.cs.  40  %   2 50  gms.  Fe. 
acetic  acid,  and  500  c.cs.  of  water,  the  whole  being  then  boiled  p  cxs. 
vigorously  for  a  few  minutes,  after  which  the  moist  nitro-acetanilide  Acetic  acid, 
is  added  slowly  in  small  portions  with  continuous  stirring  and  boiling, 
so  that  the  solution  tested  on  filter  paper  remains  colourless.    When 
all  has  been  added,  boiling  is  continued  for  a  further  ten  minutes, 
the  evaporated  water  being  replaced.    After  the  liquid  has  cooled  ca.  10  gms. 
to  70°  sufficient  soda  is  added  to  give  a  perceptible  alkaline  reaction.      aaCO3. 
The  whole  quantity  obtained  from  93  gms.  aniline  can  easily  be 
reduced  in  20  minutes.     If  boiling  be  continued  whilst  neutralizing, 
or  if  too  much  soda  be  added,  the  nitro-acetanilide  is  easily  hydro- 
lysed.    It  is  not  possible,  however,  to  precipitate  at  70°  all  the 
iron  which  has  gone  into  solution,  and  as  this  is  absolutely  necessary 
the  remainder  of  the   metal  is   precipitated  with   the   minimum 
quantity  of  ammonium  sulphide  until  a  drop  placed  on  filter  paper 
gives  no  coloration  with  alkali  sulphide.     After  this  the  mass  may 
be  filtered. 

The  solution,  freed  from  iron  and  iron  oxide,  is  now  evaporated 
down  to  400  c.cs.  over  a  bare  flame.     On  cooling,  the  amino- 


72  INTERMEDIATE  PRODUCTS 

acetanilide  separates  out  in  beautiful  long  needles.  The  yield  from 
93  gms.  aniline  is  about  75  gms.  pure  base.  The  mother-liquor,  which 
always  contains  about  15  %  of  less  pure  products,  is  evaporated 
down  further  after  standing  for  a  day,  and  is  then  again  allowed  to 
crystallize. 

The  product  so  obtained  is  sufficiently  pure  for  the  works,  but 
if  desired  absolutely  pure  it  may  be  recrystallized  from  a  little  water, 
preferably  with  the  addition  of  animal  charcoal.  The  solutions, 
which  on  the  large  scale  are  evaporated  down  in  vacuo,  yield  a  purer 
amino-acetanilide . 

On  hydrolysing  the  amino-acetanilide,  exactly  as  in  the  case  of 
mtraniline,  the  important  />-phenylene-diamine  is  obtained.  It  is 
extremely  easily  oxidized  and  is  therefore  hydrolysed  either  in 
complete  absence  of  air,  or  by  boiling  with  dilute  sulphuric 
acid. 

Notes  on  Works  Technique  and  Practice. — ^-Nitraniline  is  one  of 
the  most  important  products  of  the  aniline  dye  industry.  It  serves 
not  only  for  the  preparation  of  solid  colours  in  powder  form,  but 
also,  and  to  a  still  greater  extent,  for  the  production  of  Para  Red, 
which  is  an  azo  combination  formed  on  the  cotton  fibre  with 
j3-naphthol.  The  nitraniline  is  prepared  by  two  different  processes  ; 
the  most  important  is  that  starting  from  aniline.  The  manufacture 
of  acetanilide  is  carried  out  either  in  enamel-lined  or  in  aluminium 
vessels.  The  mother-liquors  are  worked  up  for  sodium  acetate. 
The  other  process  starts  from  ^-nitro-chlorbenzene,  which  is 
converted  into  nitraniline  on  heating  in  an  autoclave  with 
ammonia  :  x 

NH2 

-f  (NH3)HC1 
N02 

Since  very  high  pressures  are  produced  on  heating  to  200°,  many 
factories  fear  to  use  this  process,  although  it  gives  a  ^-nitraniline 
which  is  much  purer  and  just  as  cheap.  For  especially  pure  Para 
Red,  many  dyers  prefer  nitraniline  made  by  this  method,  which  is 
carried  out  successfully  in  certain  of  the  smaller  works. 

1  See  D.  R.  P.  148749. 


NITRATIONS  AND   REDUCTIONS  73 

Ortho-  and  Para-Nitrophenol  and  their  Alkyl  Ethers. 
Reaction : 


,      ,       )NO, 
OH 


O1 


AlkyJ 

OH  O 


\/ 

N02  N02 

93  Gms.  Phenol  are  melted  with  20  c.cs.  water,  and  the  liquid  93  gms. 

mixture  is  allowed  to  drip  into  a  solution  of  150  gms.  sodium  nitrate  aoc.es.' 

in  400  c.cs.  of  water  and  250  gms.  concentrated  sulphuric  acid.  H2O. 
During  the  addition  the  liquid  must  be  kept  well  stirred  and  the 


temperature  below  20°.    After  all  has  been  added,  stirring  is  con-  250  gms. 

tinued  for  a  further  2  hours.     The  mother-liquor  is   then   poured  550  %£' 

off  the  resinous  mixture  of  the  nitro  bodies,  and  the  residue  melted  4°o  c.cs. 

with  500  c.cs.  of  water  with  the  addition  of  sufficient  chalk  to  give  CaCO3. 

a   completely   neutral   reaction  with  litmus.     The   wash-liquor  is 

thrown  away  and  the  washing  repeated.     The  crude  nitrophenol 

freed  from  nitric  acid  is  now  steam-  distilled,  using  a  wide  condenser. 

About  40  gms.  of  pure  o-nitrophenol  pass  over.     The  residue  left 

in  the  flask  is  then  allowed  to  cool  down,  and  after  standing  for 

24  hours  is  filtered  off  from  the  mother-liquor.     The  residue  is 

boiled  up  with  i  litre  of  2  %  hydrochloric  acid  and  filtered  through  ca.  1000  c.cs. 

a  folded  filter.     The  pure  />-nitrophenol  crystallizes  out  from  the  2  % 

hot  solution  in  long,  practically  white  needles  ;    if  necessary,  the 

extraction  may  be  repeated. 

The  yield  is  about  40  gms.  ortho-  and  about  the  same  quantity  of 
para-derivative.  Treatment  of  the  crude  nitrophenol  with  caustic 
soda  solution  has  a  very  harmful  effect,  although  given  in  various 
recipes,  as  the  lye  has  an  immediate  resinifying  action. 

Notes  on  Works  Technique  and  Practice.  —  In  carrying  out  the 
distillation  on  the  large  scale,  either  worm  condensers  standing  in 
warm  water,  or  straight  condensers  fed  with  warm  water,  are  used, 
in  order  to  prevent  "  freezing  up."  Preferably  the  steam  is  heated 
to  110°  as  very  little  is  then  required. 

o-  and^>-Nitrophenols  are  the  starting-point  for  the  preparation  of 
o-  and  />-phenetidine,  and  for  o-  and^>-anisidine.  From  o-nitroanisol, 


74 


INTERMEDIATE  PRODUCTS 


further,  dianisidine  is  prepared,  which  gives  the  finest  direct  blue 
on  the  market  (Diamine  Pure  Blue,  Chicago  Blue,  etc.). 

Alkylation  of  the  Nitrophenols. 

Nitrophenols  are  converted  into  their  ethers  by  the  following 
general  method  : — 

i  Gm. -molecule  of  phenol  is  dissolved  in  a  mixture  of  400  c.cs. 


water,  i  gm.-molecule  caustic  soda  lye, 
and  80  gms.  soda.  To  this  solution 
are  added  500  c.cs.  methyl  (or  ethyl) 
alcohol  of  90  %  strength,  and  it  is 
then  cooled  to  10°.  1*75  Gm. -molecules 
methyl  chloride  or  ethyl  chloride  are 
then  added.  The  mixture  is  heated 
in  an  autoclave  for  8  hours  to  100° 
with  stirring  or  rotation,  at  4-5  atmos. 
The  alkylation  is  then  complete  ;  the 
product  is  poured  into  water,  the 
alkyl  ether  separated,  and  the  spirit 
rectified.  The  alkyl  derivative  is 
washed  with  a  little  lye  and  water  and 
should  then  contain  no  free  nitrophenol. 
Working  with  ethyl  or  methyl 
chloride  is  no  easy  matter,  for  which 
reason  the  most  convenient  method  is 
given  here :  the  mixture  of  nitro- 
phenol, soda  and  lye  with  aqueous 
alcohol  is  poured  into  the  autoclave 
and  the  latter  closed  ;  it  is  not  neces- 
sary to  dissolve  the  substances.  The 
autoclave  is  then  evacuated  by  means 
of  a  water-pump  and  again  closed  by 

FIG.    16.— Small  gas  cylinder     means    Qf   the    valvCg        A    small    alkyl 
made  of  gas-tube  for  adding  .  f 

alkyl  chloride.  chloride  bomb  made  from  a  piece  ot 

gas  tube  (i)  2  ins.  in  diameter  with  a 

screw  nut  (3)  is  then   joined   on   to   the  autoclave  by  means   of 
a  copper  tube  (4),  and  a  connection  (2)$  (Fig.   16).     The    alkyl 


NITRATIONS  AND   REDUCTIONS 


75 


chloride  should  previously  have  been  added  to  the  bomb  from 
a  cooled  glass  cylinder,  the  bomb  being  placed  in  ice  water  for  this 
purpose.  As  soon  as  the  alkyl-chloride  bomb  has  been  attached 
to  the  autoclave  (I),  it  is  inverted  (la)  so  as  to  permit  the  contents 


FIG.  i6A. — Method  of  filling  a  laboratory  autoclave  with  alkyl-chloride. 

to  run  down  the  tube.  It  is  now  warmed  by  means  of  a  very  hot, 
wet  cloth  until  one  can  only  just  touch  it,  after  which  the  autoclave 
valve  is  opened  (Fig.  i6A).  The  warm  alkyl-chloride  immedi- 
ately rushes  into  the  evacuated  autoclave,  the  valve  of  which  is  closed 
after  a  few  seconds.  It  has  been  shown  experimentally  that  by  this 
means  at  least  98  %  of  the  alkyl-chloride  enters  the  apparatus.  The 


76 


INTERMEDIATE  PRODUCTS 


bomb,  which  now  has  no  internal  pressure,  may  be  removed  and  the 
autoclave  warmed  in  an  oil-bath  as  described  above. 

In  the  works  alkylations  are  carried  out  in  large  horizontal  or 
vertical  boilers  (see  Chrysophenin).  The  alkyl-chlorides  are  always 
prepared  from  hydrochloric  acid,  alcohol,  and  zinc  chloride.  They 
are  transported  in  large  iron  cylinders,  and  are  stored  in  reservoirs. 
For  use  they  are  rilled  into  steel  bottles  from  which  they  are  either 
pumped  into  the  reaction  vessel,  or  forced  through  an  inlet  tube  by 
means  of  heat. 


Trinitrophenol  (Picric  Acid). 


93 
Phenol. 
300  c.cs. 
H2S04 
(ioo  %) 


440  gms. 
50% 
mixed  acid. 


Reaction  : 
OH 


OH 


OH 


Phenol. 


]S03H 


SOgH 

Disulphonic  acid. 


NO2 

Trinitrophenol. 


93  Gms.  best  quality  phenol  are  placed  in  a  glass, iron, or  porcelain 
sulphonating  pot.  It  is  warmed  to  100°  with  stirring,  and  300  gms. 
monohydrate  are  then  added,  the  temperature  being  kept  below 
110°,  and  maintained  at  100-110°  for  a  further  hour  to  ensure  the 
complete  sulphonation  of  all  the  phenol.  The  greater  portion  of 
the  phenol  is  converted  into  the  disulphonic  acid  in  this  manner. 
By  means  of  external  cooling  with  ice  and  salt,  the  contents  of  the 
beaker  are  cooled  down  to  o°,  and  to  it  are  added  drop- wise  during 
3  hours,  3'5  molecules  nitric  acid  as  50  %  mixed  acid. 

Commercial  mixed  acid  is  made  from  very  concentrated  nitric 
acid  and  highly  concentrated  oleum.  Usually  nitric  acid  of  sp.  gr. 
1*48  is  mixed  with  40  %  oleum  in  large,  water-cooled  iron  kettles. 
In  the  laboratory  this  process  is  not  carried  out  owing  to  the  great 
danger.  It  suffices  on  the  small  scale  to  mix  nitric  acid  of  sp.  gr. 
i "50-1  '52  with  its  own  weight  of  monohydrate. 

As  soon  as  all  the  nitric  acid  has  been  dropped  into  the  phenol- 
sulphonic  acid,  the  mixture  is  allowed  to  stand  over-night  at  the 
ordinary  temperature,  and  next  day  it  is  warmed  very  slowly  with 
stirring  on  the  water-bath  to  30°  during  i  hour.  The  temperature 
is  then  raised  to  45°,  but  no  higher,  otherwise  the  mass  may  suddenly 
heat  up  of  its  own  accord  ;  in  this  case,  even  if  there  is  no  explosion, 
all  the  contents  will  be  forced  out  of  the  kettle.  The  reaction, 


FIG.  20. —  General  arrangement  of  a  colour  s- 

1.  Hydraulic  press. 

2.  Filter-press  with  wooden   trays   for 

the  filter-cake. 

3.  Pressure  vat  with  iron  supports. 

4  and  5.  Wooden  vats  with  mechanical 
stirring  gear. 


PLATE   VII 


jised  in  the  dye  industry  (scale  i  :  100). 

16.  Ventilating  shaft  with  steam  jet. 

17.  Driving  shaft  and  wheel. 

J8.  Pressure  pipe  from  autoclave. 
9.  Travelling  crane  (10  tons), 
o.  Autoclave.   Capacity  i|  cubic  metres. 
i  and  12.  Hoists  (3  tons). 


NITRATIONS  AND   REDUCTIONS  77 

however,  cannot  be  completed  at  45°.     A  small  portion,  therefore, 
of  the  nitrating  mixture  (about  50  c.cs.)  is  placed  in  a  porcelain  dish 
of  1 1  litres  capacity  and  warmed,  with  stirring,  on  the  sand-bath. 
The  temperature  rises  rapidly  to  110-125°,  after  which  the  rest  of 
the  mixture  is  dropped  slowly  with  continuous  stirring  on  to  the 
pre-heated  portion,  so  that  no  frothing  over  can  take  place.     The 
heating  is  continued  for  a  further  half-hour  at  110-120°,  after  which 
sufficient  water  is  added  to  produce  a  sulphuric  acid  of  about  40  %, 
keeping  the  temperature  at  120°.     For  this  purpose  about  700  c.cs.  7ooc.cs. 
of  water  are  required,  as  may  be  easily  calculated.     Nitrous  fumes 
are  evolved,  but  only  in  small  quantities  if  the  nitration  has  been 
properly  carried  out.     The  picric  acid  separates  quantitatively  on 
cooling  as  it  is  insoluble  in  40  %  sulphuric  acid.     A  certain  amount 
of  resinous  and  other  decomposition  products  remain  in  the  mother- 
liquor.     The  picric  acid  is  filtered,  after  cooling,  through  a  cotton 
filter,  and  is  washed  with  cold  water,  after  which  it  is  chemically 
pure.     A  yield  of  about  210  gms.  pure  product  is  obtained. 

In  the  same  way  are  prepared  Martius  Yellow  (dinitronaphthol 
1:2:4),  Naphthol  Yellow  S  (dinitronaphthol  monosulphonic  acid 
1:2:4:6),  as  also  dinitro-cresol  and  other  polynitro  compounds. 
With  a  sufficient  concentration  of  the  nitrating  mixture,  practically 
the  theoretical  quantity  of  nitric  acid  will  suffice. 

Notes  on  Works  Technique  and  Practice. — All  the  liquids  mentioned 
are  strongly  acid,  and  must  therefore  be  filtered  through  acid-proof 
material :  e.g.  stone  suction  filters  (Fig.  14,  Plate  V.),  or  gun-cotton 
filter-cloths  (nitre-filters).  The  nitrous  gases  evolved  during  the 
nitration  are  condensed  to  nitric  acid  in  towers  provided  with 
Raschig-rings. 

Picramic  Acid. 

Reaction  : 


NO2  NO< 


10  Gms.  picric  acid  and  10  gms.  of  35  %  soda  lye  are  dissolved  10  gms. 

in  600  c.cs.  water  contained  in  a  glass  or  iron  vessel  holding  at  least  ^cric  acid> 

i-|-  litres.    After  heating  up  to  55°  the  liquid  is  stirred  vigorously  36  % 

and  a  solution  of  4O*gms.  crystallized  sodium  sulphide  and  100  c.cs.  ^aOHs* 

water  is  run  in,  in  a  thin  stream,  during  10  minutes.    After  the  Na2S 

+9H20. 


INTERMEDIATE  PRODUCTS 


127*5  gms. 
Picric  acid. 

220  gms. 

Na2S 

+9H2O. 


400  gms. 
Ice. 


137*5  gms. 
Picric  acid. 

36  gms. 
Soda. 
240  gms. 
Na2S 
+QH20. 

io8gms. 
HC1  (30  %). 
300  c.cs. 
H,0. 


2000  C.CS. 

Water. 
70  c.cs. 

30% 
HC1  + 
400  c.cs. 
H20. 


addition,  127*5  gms-  °f  powdered  picric  acid  are  scattered  in,  about 
a  teaspoonful  at  a  time,  a  solution  of  220  gms.  sodium  sulphide  in 
400  c.cs.  water  being  allowed  to  run  in  simultaneously  during 
10  minutes.  The  addition  of  the  picric  acid  should  end  just  at  the 
same  time  as  that  of  the  sodium  sulphide.  If  the  temperature 
should  exceed  65°  a  little  ice  must  be  added.  After  all  has  been 
added,  stirring  is  continued  for  a  further  10  minutes,  after  which 
400  gms.  of  ice  are  added  quickly,  whereupon  the  sodium  salt  of 
the  picramic  acid  is  completely  precipitated  at  once.  After  standing 
10  hours  it  is  filtered  off  and  washed  with  10  %  brine.  The  free 
picramic  acid  is  obtained  by  stirring  up  the  sodium  salt  with  500  c.cs. 
of  water,  warming  to  80°,  and  acidifying  with  dilute  sulphuric  acid 
until  just  acid  to  Congo.  After  cooling  and  standing  for  10  hours  the 
product  is  filtered  off,  the  yield  being  about  loogms.  of  100  %  product. 

Modification. — The  partial  reduction  of  picric  acid  can,  of  course, 
be  carried  out  in  various  ways.  Thus,  instead  of  making  the 
addition  gradually  and  so  neutralizing,  as  it  were,  the  resultant 
alkali  with  this  acid,  the  sodium  salt  may  be  reduced,  the  requisite 
quantity  of  hydrochloric  acid  being  run  in  simultaneously. 

For  instance,  6-10  gm.-molecule  (=137*5)  picric  acid  are 
dissolved  in  1200  c.cs.  water  at  50°  with  the  aid  of  36  gms.  soda  ; 
complete  solution,  however,  is  not  effected.  When  the  carbon 
dioxide  has  been  driven  off,  i  gm.-molecule  (=240  gms.)  crystallized, 
sodium  sulphide  dissolved  in  450  c.cs.  water  is  run  in  during  half 
an  hour  with  good  stirring.  At  the  same  time  a  mixture  of  108  gms., 
30  %  HC1,  and  300  c.cs.  water  is  run  in  so  that  the  acid  takes  about 
a  minute  longer  than  the  sodium  sulphide.  After  all  has  been 
added,  stirring  is  continued  for  half  an  hour  without  heating,  the 
mixture  allowed  to  stand  for  12  hours  and  filtered.  The  precipitate 
is  washed  with  100  c.cs.  saturated  brine.  The  crude  sodium 
picramate  is  dissolved  in  2  litres  water,  and  the  filtered  solution 
poured  into  a  dilute  hydrochloric  acid  made  up  of  70  c.cs.  of 
30  %  hydrochloric  acid  and  400  c.cs.  water  at  90°.  The  pure 
picramic  acid  is  completely  precipitated  within  24  hours  ;  it  is  then 
filtered  off  and  washed  with  a  little  water,  after  which  it  is  pressed 
and  dried  at  80°,  the  yield  being  about  100  gms.  =  83  %  of  theory. 

On  the  works  scale  the  former  of  the  two  methods  given  is  the 
more  satisfactory,  as  the  gradual  addition  of  the  substances  can  be 
better  regulated. 

In  recent  years  picramic  acid  has  become  very  important  as 
an  azo  component.  It  gives  very  fast  wool  colours  which  are 
distinguished  by  the  fact  that  they  can  be  dyed  with  the  aid  of 


NITRATIONS   AND   REDUCTIONS  •  79 

chromic  acid.     Examples  of  these  are  the  Metachrome  colours  of 
the  Berlin  Aniline  Co.,  e.g.  Metachrome  Brown  : 

OH  NH^ 

N02/\— N2— /"  ~\NH  .  CH2  .  COOH 

V 
N02 

For  the  most  part  these  dyes  are  difficultly  soluble  in  water  and 
in  the  dry  state  are  often  explosive,  for  which  reason  they  must 
either  be  ground  up  with  a  large  quantity  of  Glauber  salt,  or  placed 
on  the  market  as  aqueous  pastes. 

The  diazo  compound  of  picramic  acid  was  the  first  example  of 
this  class  of  substances  to  be  discovered,  and  led  to  the  important 
researches  of  Peter  Griess. 


a-Nitronaphthalene  and  a-Naphthylamine.1 
Reaction :  NQ 


The  nitration  of  naphthalene  takes  place  very  vigorously  so 
that  poly-nitro  products  are  readily  obtained.  The  naphthalene 
used  should  be  extremely  pure  as  otherwise  the  yields  are  unfavour- 
ably influenced.  If  no  satisfactory  naphthalene  is  obtainable,  it  is 
advisable  to  purify  some  by  distillation  and,  if  necessary,  by  subse- 
quent heating  with  5  %  of  its  weight  of  concentrated  sulphuric  acid. 
As  the  nitration  must  be  performed  at  a  temperature  below  the 
melting-point  of  the  naphthalene,  the  substance  must  be  finely 
powdered  (to  pass  through  a  sieve  with  400  meshes  per  sq.  cm.), 
as  larger  particles  would  escape  the  action  of  the  nitric  acid. 

128  Gms.  naphthalene  are  added  to  a  mixture  of  103  gms.  nitric  128  gms 
acid  of  60  %  (40°  Be.),  and  300  gms.  of  80  %  sulphuric  acid. 
Stirring  is  continued  without  interruption  for  6  hours  at  50°,  the  HNO3, 
temperature  being  finally,  increased  to  60°  during   i   hour,  after  4°° B6- 
which  it  is  cooled  down.     The  nitronaphthalene  floats  upon  the  H2SO4 
surface  of  the  acid  in  porous  cakes,  and  consists  of  about  95  %  a-nitro  8o  %• 
compound,  together  with  some  unchanged  naphthalene  and  a  very 
little   dinitro   derivative.     j8-Nitronaphthalene  is   either   absent  or 
present  only  in  traces. 

1  See  also  O.  N.  Witt,  Chem.  Ind.  (1887),  215  ;  S.  Paul,  Z.f.a.  Ch.  (1897),  145. 


8o*  INTERMEDIATE  PRODUCTS 

The  crude  product  is  melted  up  several  times  with  boiling  water 
by  which  means  the  acid  is  completely  removed  and  the  naphthalene 
carried  off  by  the  steam.  The  melted  product  is  then  poured  into 
cold  water,  which  is  kept  well  agitated,  the  nitronaphthalene  separating 
out  in  the  form  of  small  spheres. 

To  obtain  the  compound  completely  pure,  it  is  dried  by  melting 
it  at  120°  in  an  air  oven.  It  is  then  treated  with  10  %  of  its  weight 
of  ligroin  (b.p.  about  150°),  or  crude  xylene  or  cymene  may  be 
used  instead.  It  is  then  filtered  hot  through  a  smooth  filter 
and  allowed  to  stand  in  a  closed  vessel  for  some  time.  A  crystalline 
cake  is  formed  which  is  well  pressed  out  in  a  cotton  cloth.  This 
purification  should  be  repeated  until  the  nitronaphthalene  shows  a 
melting-point  of  61°.  It  is  thus  obtained  in  the  form  of  yellow, 
glistening  crystals.  A  considerable  portion  of  the  nitronaphthalene 
always  remains  behind  in  the  mother-liquors  and  may  be  recovered 
by  distilling  off  the  solvent. 

Crude  nitronaphthalene  is  reduced  by  Bechamp's  method  by 
means  of  iron  and  a  little  hydrochloric  acid  ;  the  mixture  must  not, 
however,  be  heated  too  high  or  else  too  much  naphthalene  will  be 
formed  ;  but  it  is  not  possible  to  prevent  this  reaction  altogether, 
as,  for  instance,  in  the  preparation  of  aniline,  although  in  the  latter 
case  its  effect  is  but  slight. 

200  gms  Fe          2O°  Gms.  iron  turnings,  100  gms.  water,  and  10  c.cs.  of  30  % 

ioo  gms.         hydrochloric  acid  are  placed  in  an  iron  reducing  pot,  fitted  with 

an  "  anchor  "  stirrer.    As  soon  as  the  evolution  of  hydrogen  has 

30  (%  '  ceased  at  50°  the  nitronaphthalene  is  added  in  small  portions,  taking 


care,  by  means  of  external  cooling,  that  the  temperature  rises  no 
higher.  One  gm.-molecule  (=173  gms.)  nitronaphthalene  (calcu- 
thalene.  lated  as  air-dried  substance)  is  reduced  within  4  hours,  with  con- 
tinuous stirring.  It  is  inadvisable  to  proceed  more  quickly  or 
undesired  azo  compounds  may  be  formed.  The  mixture  is  now 
treated  with  enough  soda  to  give  a  distinctly  alkaline  reaction, 
after  which  the  contents  of  the  reduction  vessel  are  transferred  to  a 
basin.  The  separation  of  the  a-naphthylamine  formed  is  best 
effected  even  in  the  laboratory  by  distilling  with  super-heated  steam, 
for  which  purpose  the  whole  reduction  product  together  with  water, 
iron,  and  iron  oxide  are  placed  in  the  oil-heated  pot  shown  in 
Fig.  36,  Plate  XIV.  The  water  is  distilled  off  completely  with 
continuous  stirring  by  heating  the  oil-bath  to  200°,  after  which 
super-heated  steam  at  250°  is  blown  in  (Fig.  ly).1 

The  illustration  is  diagrammatic  and  does  not  show  the  stirrer.     In  order  to 
e  the  easy  separation  of  t 
the  mixture  to  be  kept  stirred. 


ensure  the  easy  separation  of  the  iron  oxide  and  naphthylamine,  it  is  advisable  for 
be  ke 


NITRATIONS  AND  REDUCTIONS 


81 


t 

t>. 

M 

CD 
£ 


82  INTERMEDIATE  PRODUCTS 

If  the  distillation  is  carried  out  properly,  it  is  possible  to  distil 
over  half  to  one  part  naphthylamine  for  each  part  water.  A  small 
amount  of  finely  divided  iron  powder,  graphite  from  the  cast-iron, 
and  iron  oxide,  are  always  carried  over  with  the  base.  As  soon  as 
the  point  is  reached  at  which  the  steam  at  260°  carries  over  only 
discoloured  products  or  none  at  all,  the  distillation  is  complete  ; 
it  should  ccupy  from  i-i  J  hours  according  to  the  method  of  heating. 
There  rema'ns  in  the  kettle  a  black  very  finely  divided  mass,  which 
is  pyrophorous,  and  therefore  must  not  simply  be  thrown  away. 
After  cooling,  the  naphthylamine  is  separated  from  the  mother- 
liquor,  melted,  and  dried  at  no0  in  the  air  oven,  after  which  it  is 
vacuum-distilled.  The  base  is  obtained  as  a  completely  colourless 
crystalline  product.  The  yield  from  i  gm.-molecule  of  naphthalene 
is  about  no  gms.  pure  a-naphthy famine.  M.p.  50°. 

Notes  on  Works  -Practice. — (a)  Nitronaphthalene.  A  portion 
of  the  waste  nitrating  acid  is  always  made  use  of  again  by  simply 
making  up  to  80  %  by  the  addition  of  stronger  sulphuric  acid. 
The  residue  is  used  for  acidifying  alkali  melts,  etc.  With  correct 
grinding  (disintegration  at  60°)  it  is  possible  to  obtain  practically 
quantitative  yields  in  the  nitration.  The  nitronaphthalene  is  also 
used  for  the  preparation  of  1:5 -nitronaphthalene  and  1:5  naphthyl- 
amine sulphonic  acids.  Further,  the  nitronaphthalene  has  been 
applied  (first  by  the  B.A.S.F.)  to  the  preparation  of  the  diazo  com- 
pound of  aminonaphthol  sulphonic  acid  1:2:4;  on  heating  with 
sodium  sulphite^  it  yields  naphthylamine  disulphonic  acid  1:2:4, 
together  with  some  naphthionic  acid  ;  the  former  can  be  diazotized 
and  converted  into  the  diazo  compound  of  the  above  mentioned 
sulphonic  acid  on  treatment  with  sodium  bicarbonate  and  sodium 
hypochlorite.  The  following  scheme  illustrates  the  course  of  this 
curious  reaction  (see  D.  R.  P.  160536) : 

NH2  N2\ 

/\SO,Na  /\/\SO3    +HOCI 


HCl+NaN02  \/\/  NaHCO, 

S03Na  S03Na  SO3Na 

NH, 


S03H 


CHLORINATIONS  83 

Although  this  process  is  quite  satisfactory  it  has  been  replaced 
by  the  still  cheaper  Sandmeyer  method. 

(b)  a-Naphthylamine.  The  reduction  is  carried  out  in  a  similar 
apparatus  to  that  which  has  already  been  described  on  several 
occasions.  But  owing  to  the  stiff,  porridgy  consistency  of  the  reduc- 
tion liquid,  it  is  not  possible  to  use  a  plough-  or  propeller-stirrer, 
but  the  "  anchor  "  type  must  be  utilized,  such  as  that  given  in 
Plate  II.  The  steam  distillation  is  effected  in  an  apparatus  similar 
to  that  indicated  in  Fig.  19.  The  incoming  steam  is  almost  in- 
variably pre-heated  in  a  special  superheater.  Satisfactory  apparatus 
of  this  type  is  supplied  by  various  makers. 


3.    CHLORINATIONS 

Chlorbenzene  and  Dinitrochlorbenzene  from  Benzene. 

Reaction  : 


+  Cl2+Fe       '      x 


Cl 


Cl 


Cl 


,. ,  N0< 

a  little 

y 


NO 


On  the  works  scale  the  introduction  of  chlorine  and  bromine 
into  aromatic  hydrocarbons  is  carried  out  almost  exclusively  by 
direct  halogenation.  Only  in  very  special  cases  is  the  Sandmeyer 
reaction  used,  as,  for  instance,  in  the  case  of  the  chlorbenzaldehydes, 
for  which  purpose  the  pure  chlortoluenes  are  best  made  from  the 
corresponding  tqluidines  (see  p.  91). 

Benzene  readily  takes  up  chlorine  in  the  presence  of  carriers  ; 
iron  is  the  only  catalyst  of  practical  importance.  In  this  case  the 
best  iron  for  the  purpose  is  not  cast-iron,  but  wrought-iron,  as  it 
acts  less  vigorously. 

600  Gms.  of  pure  dry  benzene  are  heated  to  boiling  with  5  gms.  600  gms. 
of  wrought-iron  powder  in  a  litre  bolthead  fitted  with  a  reflux  con- 
denser  ;    a  slow  stream  of  dry  chlorine  is  then  passed  through  at 
79°  with  vigorous  stirring  (Figs.  18  and  i8A).     The  chlorine  must 
always  be  carefully  dried  by  means  of  at  least  three  wash-bottles  1 

1  The  so-called  "  Spiral  "  wash-bottles,  in  which  the  gas  bubbles  are  com- 
pelled to  follow  a  long  spiral  course  through  the  sulphuric  acid,  are  strongly 
recommended. 


84 


INTERMEDIATE  PRODUCTS 


and  a  calcium  chloride  tube,  as  any  trace  of  moisture  encourages 
side  reactions. 

The  hydrochloric  acid  evolved  during  the  addition  is  led  into  a 
flask  containing  a  layer  of  water  which  absorbs  the  hydrochloric 
acid  gas  practically  completely.  The  inlet  tube  should  not  touch 
the  surface  of  the  liquid  or  else  the  water  will  be  immediately  sucked 
back  into  the  chlorinating  flask.  Chlorine  is  passed  in  until  about 
90  %  of  the  calculated  quantity  has  been  used  up.  If  an  excess  be 


FIG.  18. — Stirring  by  means  of  Witt's  bell- 
stirrer. 


FIG.  i8A. — Heating  under  a 
reflux  condenser,  and 
stirring,  with  an  ordinary 
bulb  condenser. 


260  gms. 
increase  in 
weight  =  5  20 
gms. 
Chlorine. 


used  too  much  dichlorbenzene  is  produced,  which  hitherto  has 
found  use  only  as  a  moth-preventive.  The  chlorination  of  600  gms. 
benzene  lasts  about  5  hours  and,  altogether,  sufficient  chlorine 
should  be  used  to  cause  an  increase  in  weight  of  260  gms.  ;  the  gas 
must  not  be  passed  in  too  rapidly  or  else  too  much  benzene  will  be 
carried  off,  which  must  be  allowed  for  in  the  calculation.  If  the 
inlet  tube  should  become  stopped  up  with  dichlorbenzene,  the 


CHLORINATIONS  85 

stream  of  chlorine  is  interrupted  for  a  short  time,  when  the  dichlor 
product  will  rapidly  dissolve  again. 

When  the  chlorination  is  complete,  the  product  is  allowed  to 
stand  for  some  time  and  is  then  poured  off  from  the  iron  sludge. 
The  mixture  is  rectified  by  means  of  a  fractionating  column  at  least 
30  cms.  long,  filled  with  glass  beads.  Approximately  the  following 
fractions  will  be  obtained  : — 

B.P.  %  Composition. 

79-81°  3  Benzene. 

81-125°  10  Benzene  and  Chlorbenzene. 

126-133°  85  Chlorbenzene. 

133-180°  5  Chlorbenzene  and  Dichlorbehzene. 

5  Resinous  matters  and  loss. 

The  fraction  boiling  at  126-133°  is  re-distilled  through  the 
column,  700  gms.  of  pure  chlorbenzene  of  b.p.  131-132°  being  finally 
obtained.  The  yield,  calculated  on  the  benzene  actually  used  up,  is 
about  90  %. 

Notes  on  Works  Practice. — Chlorbenzene  has  become  an  im- 
portant intermediate  for  various  other  compounds  (cf.  dinitrochlor- 
benzene).  It  is  produced  in  quantities  of  2  tons  or  more  at  a  time, 
in  cast-iron  vessels  provided  with  stirring  gear  and  reflux  condenser. 
The  rectification  is  carried  out  very  carefully,  the  Kubierschky 
columns  coming  more  and  more  into  use  for  this  purpose,  as  they 
are  far  more  efficient  than  the  older  types.  The  vapours  run  through 
the  entire  length  of  the  column  almost  without  resistance,  and  are 
thoroughly  washed  out  ("  dephlegmated ")  by  the  descending 
current  of  liquid.  Other  forms  of  column  are  also  used  such  as  the 
cheap  and  effective  Raschig  column,  in  which  the  gases  pass  through 
a  tower  filled  with  short  cylinders  possessing  the  same  height  and 
diameter.  These  rings  therefore  lie  quite  irregularly  in  the  tower, 
and  give  a  large  surface  without  offering  much  resistance.  Plate  IX. 
shows  rectifying  columns  of  these  types  which  can  also  be  erected 
for  continuous  service.  It  is  possible  to  effect  the  separation  so  com- 
pletely that  the  yield  of  pure  distillate,  calculated  upon  the  benzene 
used,  rises  to  96  % .  The  hydrochloric  acid  evolved  in  such  chlorina- 
tions  is  condensed  in  the  well-known  stoneware  Woulf  bottles. 
The  small  amount  of  chlorine  present  is  neutralized  by  the  addition 
of  a  little  sodium  bisulphite.  This  "  chlorination-hydrochloric 
acid  "  is  cheap  and  very  pure,  and  plays  an  important  role  in  the 
colour  factories. 


86  INTERMEDIATE  PRODUCTS 


Dinitrochlorbenzene  from  Chlorbenzene. 

The  nitration  of  chlorbenzene  takes  place  very  readily  ;  it  is 
nitrated  first  only  to  the  mono-nitro  stage,  as  given  under  the  prepara- 
tion of  dinitrobenzene.  The  product  is  a  mixture  of  ortho-  and  para- 
derivatives  which  is  not  easy  to  separate  as  their  boiling-points  are 
very  close  to  one  another,  namely,  243°  and  242°  for  the  ortho-  and 
para-  compounds  respectively. 

For  this  reason  the  separation  is  always  effected  by  freezing  out, 
centrifuging  and  distilling  in  vacuo  with  a  very  tall  column.  This 
operation  cannot  be  properly  carried  out  in  the  laboratory,  but  it  is 
quite  easy  to  separate  a  large  portion  of  the  para  product  in  a  pure 
condition  from  the  crude  mixture  of  the  two  nitrochlorbenzenes  by 
freezing  out  and  pressing.  The  nitrochlorbenzenes  are  very 
poisonous,  for  which  reason  the  centrifuges  in  which  the  product  is 
"  whizzed  "  must  be  very  carefully  built,  provided  with  well-fitting 
covers  with  flues  similar  to  those  in  which,  for  instance,  gun-cotton 
is  dehydrated  by  means  of  alcohoL 

We  will  therefore  not  discuss  the  preparation  of  the  mono- 
nitro  compounds,  but  will  proceed  directly  with  the  further  nitration 
of  the  mixture. 

350  gms.  350  Gms.  of  mixed  acid  containing  50  %  HNO3  are  placed  in 

mixed  acid  an  jron  nitrating  vessel  (Fig.  2),  and  into  this  is  dropped  113  gms. 
HNO°3).  chlorbenzene  with  good  stirring,  keeping  the  temperature  below  5°. 
113  gms.  After  all  has  been  added  the  stirring  is  continued  for  a  further  hour 
benzene  at  5~IO°-  The  temperature  is  then  raised  slowly  to  50°,  and  kept 
350  gms.  f°r  a  further  hour  at  this  temperature.  350  Gms.  concentrated 
.  H2SO4  sulphuric  acid  are  then  dropped  in  very  cautiously  with  continued 
vigorous  stirring,  the  mixture  being  finally  heated  for  half  an  hour 
at  115°.  After  cooling,  the  nitrated  product  is  poured  into  2  litres 
of  water,  in  which  it  immediately  solidifies  to  a  pale  yellow  cake. 
This  is  separated  from  the  mother-liquor,  melted  under  water  to 
remove  all  acid,  and  is  then  chemically  pure.1 

The  yield  is  200  gms.  from  113  gms.  chlorbenzene.  M.p.  51°. 
Notes  on  Works  Technique  and  Practice. — The  manufacture  of 
dinitrochlorbenzene  has  assumed  quite  unexpected  proportions.  It 
serves  for  the  preparation  of  Sulphur  Black  T  (q.v.)  and  other 
important  dyes.  Further,  it  is  the  starting-point  for  a  whole  series  of 
condensation  products  which  are  obtained  by  replacing  the  mobile 

1  It  is  advisable  to  offer  a  word  of  warning  as  to  the  extremely  unpleasant 
properties  of  dinitrochlorbenzene.  Both  as  a  solid  and,  more  especially,  in  its 
solutions  it  produces  eczema  and  unbearable  itching. 


CHLORINATIONS  87 

chlorine  atom  by  basic  and  other  radicals.  Thus,  for  instance, 
hexanitrodiphenylamine  is  obtained  from  it,  which  is  one  of  the 
most  powerful  of  present-day  explosives  (torpedoes).1  Further, 
dinitraniline,  dinitrophenol,  and  picric  acid  can  be  readily  obtained 
from  it.  The  diagram  given  below  shows  only  a  small  portion  of 
the  various  practical  possibilities. 


Picric  acid.2 


\y 

N02 

Nitro-aminophenol  (see  p.  66). 


HNO, 


^  NH  \ 
N02/\N02    NO2/\NOc 


N02 

Dinitrodiphenylamine . 


'2  N°2 

Hexan  itrodiphenylamin  e . 


We  have  seen  that  in  the  laboratory  a  30  %  excess  of  nitric  acid 
is  used  in  order  to  obtain  smoother  nitration.  On  the  large  scale 
it  is  possible  to  manage  with  a  much  smaller  excess,  and  even  this 
is  finally  recovered  by  separating  the  waste  acid  into  sulphuric  and 
nitric  acids  in  denitrating  towers  by  means  of  steam.  Dinitro- 
chlorbenzene  costs  less  than  90  centimes  per  kilo. 


Benzalchloride  and  Benzaldehyde  from  Toluene. 

Reaction  : 


CH9Cf 


CCl: 


1  For    manufacture,    cf.    Zeitschr.  f.  das    Gesamte  Spreng  und  Schiesswesen 
(1913),  8,  205  and  251  (Carter). 

2  Picric  acid  may  also  be  prepared  via  picryl  chloride. 


88 


455 
Toluene. 
10  gms. 
PC15. 
355  gms. 
Chlorine 
(increase  in 
weight). 


INTERMEDIATE  PRODUCTS 
CHC12 

H2O+Fe 


161  gms. 
C6H5.CHC12. 
o's  gm.  Fe. 

25  gms. 
H20. 


About 
20  gms: 
Na2C03. 


About 
300  gms. 
NaHSO3 
(25  %  S02). 


H20+Fe 


Benzalchloride. — 455  Gms.  (=5  mols.)  dry  toluene  and  10  gms. 
phosphorus  pentachloride  are  heated  to  boiling  in  a  i -litre  bolthead 
provided  with  stirrer  and  reflux  condenser,  and  dry  chlorine  is 
passed  in  until  the  increase  in  weight  is  355  gms.1 

This  takes  about  6  hours.  The  resultant  mixture  of  unchanged 
toluene,  benzyl-,  benzal-  and  benzotri-chlorides  is  rectified  with  a 
glass-bead  column  and  the  fraction  between  160  and  225°  collected 
separately.  Its  chief  component  is  benzalchloride,  boiling  at  204°, 
together  with  a  little  benzylchloride  and  benzotrichloride.  In  the 
factory  it  is  possible  to  separate  these  components  satisfactorily 
by  careful  fractionation. 

Benzaldehyde. — The  benzalchloride  used  for  the  preparation 
of  benzaldehyde  must  be  free  from  benzylchloride,  and  must  there- 
fore first  be  very  carefully  rectified,  the  portion  passing  over  below 
1 80°  being  rejected. 

161  Gms.  (=i  mol.)  benzalchloride  containing  a  little  benzo- 
trichloride is  heated  to  30°  in  a  small  glass  bolthead  with  J  gm.  iron 
powder  during  half  an  hour,  with  stirring.  25  C.cs.  water  are  then 
added  and  the  mixture  heated  cautiously  until  evolution  of  hydro- 
chloric acid  begins  (at  about  100°).  The  reaction  now  proceeds  by 
itself  for  a  certain  length  of  time,  and  is  completed  by  gentle  warming. 
Sufficient  soda  is  then  added  to  turn  litmus  blue  and  the  benzaldehyde 
is  distilled  over  with  steam.  After  filtering,  the  residue  in  the 
flask  is  made  permanently  mineral  acid  by  means  of  hydrochloric 
acid,  when  the  benzoic  acid  formed  comes  out  in  a  pure  white  form 
on  cooling.  The  steam  distillate  contains  certain  other  products 
besides  benzaldehyde  which  cannot  be  completely  removed  by 
fractional  distillation.  It  is  therefore  dissolved  in  bisulphite  con- 
taining 25  %  SO2  and  separated,  after  standing,  from  the  oily 
portion.  250-350  Gms.  sodium  bisulphite  are  required  according 
to  the  amount  of  water  present.  The  clear  liquid  is  treated  with 

1  Sunlight  or  "  Uviol-light  "  facilitates  the  smooth  chlorination  in  the  side 
chain  to  a  remarkable  degree,  particularly  in  the  case  of  the  chlortoluenes  (cf. 
p.  90  et  seq.). 


CHLORINATIONS  89 

soda  or  caustic  soda  solution  until  distinctly  alkaline,  after  which 
it  is  separated  in  a  separating  funnel  and  distilled  finally  under 
ordinary  pressure.  The  yield  of  benzoic  acid  is  about  12  gms.,  that 
of  benzaldehyde  up  to  80  gms.  (b.p.  178-179°). 

Notes  on  Works  Technique  and  Practice. — In  contrast  to  benzene, 
toluene  cannot  be  chlorinated  in  iron  vessels  as,  in  the  presence 
of  iron,  chlorine  enters  the  benzene  nucleus.  One  is  therefore 
forced  to  use  enamelled  or  glass  vessels  for  such  chlorinations  (cf. 
dichlorbenzaldehyde,  p.  92  et  seq.).  The  addition  of  phosphorus 
pentachloride  is  frequently  omitted  as  it  has  only  an  accelerating 
action,  and  is  not  therefore  essential.  The  decomposition  of  the 
benzalchloride  is  effected  in  copper  apparatus  and  the  separation 
of  the  benzaldehyde  is  done  in  large  lead-lined  separating  funnels 
provided  with  observation  windows.  The  method  described  above 
(D.  R.  P.  85493)  nas  completely  displaced  the  older  process  starting 
from  benzylchloride,  which  was  converted  into  benzaldehyde  by 
means  of  water  and  lead  nitrate. 

There  is,  however,  another  process  which  is  carried  out  on  a 
large  scale,  and  which  favours  the  formation  of  benzoic  acid,  the 
more  expensive  product.  It  consists  in  oxidizing  toluene  in  con- 
centrated sulphuric  acid  with  pyrolusite  or  manganite  (see  Xylene 
Blue  VS.). 

Benzaldehyde  is  not  only  an  intermediate  for  various  dyes,  but 
is  used  to  an  even  greater  extent  for  scenting  the  so-called  "  Milk 
of  Almonds  "  soap  ("  Mandelmilch  Seife  ").  The  cheaper  varieties 
of  this  soap  are,  however,  adulterated  with  nitrobenzene  ("  Oil  of 
Mirbane  "),  which  may  be  recognized  by  the  fact  that  the  soap 
becomes  yellow  in  time. 


2:6-Dichlorbenzaldehyde   from    Orthonitrotoluene. 

Reaction  : 

CH3 

NiX/iX  n  MWL/i\ri  r-i< 

,  -,  _  *      • 

\/  \/  \/ 

CHC12  CHO 

_^     C1/\C1 

2 :6-Dtchlorbenataldehyde . 


9o 


INTERMEDIATE  PRODUCTS 


137  gms. 

o-Nitrotolu- 

ene. 

76  gms. 
(38  gms.) 
C12. 

20  gms.  Fe. 


(a)  Chlornitrotoluene  from  Orthonitrotoluene . 

Iron  is  the  best  catalyst  for  facilitating  the  introduction  of 
chlorine  into  orthonitrotoluene,  in  particular  the  so-called  steel 
shavings  used  for  household  purposes.  The  action  of  iron  filings 
and  grey  cast-iron  borings  is  too  energetic,  so  that  besides  2:6-chlor- 
nitrotoluene  a  considerable  quantity  of  2:5-dichlortoluene  is  formed 
(up  to  50  %),  which  does  not  yield  a  good  colour. 

Into  a  half- litre  bolthead  is  introduced  i  gm.-molecule  (=  137  gms.) 
of  carefully  dried  orthonitrotoluene  together  with  20  gms.  steel 
turnings  in  small  pieces,  and  dry  chlorine  is  passed  in  with  vigorous 
stirring  until  the  increase  in  weight  amounts  to  exactly  38  gms. 
The  temperature  rises  to  40°,  the  chlorine  absorption  occupying 
about  three  hours.  The  product  is  allowed  to  stand,  filtered  from 
iron  sludge,  and  the  crude  product  distilled  in  vacuo.  At  n  mms. 
pressure  the  following  fractions  are  obtained  : — 


100-107 
107-114' 


about  3  gms. 
about  152  gms, 


The  resinous  product  left  behind  weighs  about  8  gms. 

If  it  is  desired  to  purify  the  product  it  may  be  submitted  to  a 
further  vacuum  distillation  with  a  glass-bead  column.  The  chlor- 
nitrotoluene  so  obtained  still  contains  about  10  %  of  2:5-  and 
z:5:6-derivatives  which  cannot  be  readily  removed.  The  yield  is 
about  94  %.  By  taking  a  10  %  excess  of  chlorine,  the  2:5~dichlor- 
toluene  is  converted  for  the  most  part  into  the  2:5:6-trichlortoluene, 
which  has  practically  the  same  properties  as  the  2:6  product.1 


100  gms. 

Nitrochlor- 

toluene. 


(b)  2:6-Chlortolmdine. 


The  reduction  of  nitrochlortoluene  is  done  by  Bechamp's  method. 
100  Gms.  of  the  nitro  compound  are  added  during  2  hours  to  100  gms. 
ioo  gms.  Fe.  finely  divided  iron,  20  gms.  crude  hydrochloric  acid,  and  200  c.cs. 
water  at  the  boil  with  continuous  stirring.  The  apparatus  is  then 
placed  in  an  oil  bath,  20  gms.  of  soda  are  added  and  the  chlortoluidine 
distilled  off  with  steam  at  140°  through  an  inclined  condenser,  the 
temperature  of  the  bath  being  200°.  It  is  quite  easy  to  drive  all 
the  base  over  with  three  parts  of  water  at  most.  The  product  is 


200  C.CS. 

H2O. 

20  gms.  HC1 

(30  %)• 

20  gms. 

Na2C03. 


1  The  assumption  by  Jansen  (Chem.  Zeutr.  mo,  1900),  that  the  2:6-dichlor- 
toluene  exists  in  two  modifications  is  incorrect.  The  supposed  isomer  is  merely 
2 15  -nitrochlortoluene . 


PLATE   VIII, 


CHLORINATIONS  91 

then  removed  with  a  separating  funnel.  Purification  is  effected  by 
vacuum  distillation,  the  boiling  point  at  10  mms.  being  105-110°, 
or  240°  at  the  ordinary  pressure.  The  distillation  is  not  absolutely 
necessary  but  is  advisable  in  order  to  remove  all  the  iron.  The 
yield  is  about  94  %  of  theory. 

(c)  2:6-Dichlortoluene. 

i  Gm.-molecule  (=160  gms.)  of  chlortoluidine  is  dissolved  at  80°  160  gms. 
in  i  litre  of  water  and  450  gms.  30  %  hydrochloric  acid,  and  the  ^?rtolul~ 
solution  is  allowed  to  cool  to  30°  with  stirring.     Sufficient  ice  is  450  gms 
then  added  to  reduce  the  temperature  to  5°  (a  portion  of  the  hydro-  3°  %  HCl. 
chloride  coming  out  of  solution),  and  the  whole  is  then  diazotized   *  lltre  HaO 
with  70  gms.  of  100  %  sodium  nitrite,  dissolved  in  200  c.cs.  of  water  ^a^s' 
(see  general  instructions).     The  temperature  may  be  allowed  to  rise  200  c  cs 
to   1 6°,  the  volume  occupying  about  1*4  litres.     As  soon  as  the  H2O. 
reaction  with  nitrite  pap^r  persists  after  10  minutes,  the  diazotization 
may  be  regarded  as  complete.     The  diazonium  solution  is  now 
allowed  to  run  into  a  cuprous  chloride  solution  during  half  an  hour, 
the  requisite  solution  being  made  from  200  gms.  copper  sulphate  200  gms. 
and  200  gms.  common  salt  dissolved  in  800  c.cs.  water  by  passing  C^SQ4' 
in    sulphur   dioxide  ;    the  excess  of  SO2  must  first  be  removed  2002gms 
from  the  solution  by  boiling.1  NaCl+SO2 

The  copper  solution  is  best  boiled  up  in  an  earthenware  pot  by 
passing  in  steam,  the  diazonium  solution  being  added  with  mechanical 
stirring.  To  prevent  loss  of  dichlortoluene  the  vessel  must  be  well 
covered  in  and  the  temperature  must  not  exceed  95°.  The  resultant 
solution  is  then  placed  in  a  4-litre  flask  and  the  dichlortoluene 
driven  over  with  steam.  Approximately  160  gms.  are  obtained, 
i.e.  88  %  of  theory,  but  the  resultant  product  is  not  sufficiently  pure. 
It  is  therefore  first  shaken  in  a  separating  funnel  with  5  %  sulphuric 
acid  (66°  Be.)  after  which  it  is  washed  with  water,  then  purified  twice 
with  40  %  caustic  soda  lye,  and  finally  it  is  distilled.  It  comes  over 
at  185-192°  ;  at  192-199°  a  further  fraction  of  isomers  is  obtained, 
most  of  which  can  be  worked  up  further  with  the  main  fraction. 
The  yield  of  absolutely  pure  dichlortoluene  is  about  70  %,  calculated 
upon  nitrotoluene. 

1  The  cuprous  chloride  solution  may  also  be  prepared  in  the  following  manner  : 
100  gms.  copper  sulphate  are  dissolved  in  half  a  litre  of  water,  the  copper  is  com- 
pletely precipitated  by  the  addition  of  50  gms.  zinc  dust,  and  the  supernatant  liquid 
is  then  poured  off.  The  finely  divided  copper  is  warmed  with  dilute  hydrochloric 
acid  until  all  the  zinc  is  dissolved,  after  which  100  gms.  common  salt  and  a  further 
solution  of  100  gms.  copper  sulphate  are  added,  and  the  whole  warmed  to  80°  for 
quarter  of  an  hour. 


INTERMEDIATE  PRODUCTS 


160  gms. 
Dichlor- 
toluene. 

142  (71)  gms. 
Chlorine. 


(d)  2:(>-Dichlorbenzal  chloride. 

The  chlorination  of  dichlortoluene  to  dichlorbenzal  chloride  is  a 
very  simple  matter  in  the  laboratory.  Chlorine  is  passed  into  the 
dry  boiling  dichlortoluene,  if  possible  in  sunlight,  until  the  increase 
in  weight  is  71  gms.  for  160  gms.  of  dichlortoluene.  With  this 
quantity  the  chlorination  is  easily  completed  in  2  hours.  The  vessel 
must  be  provided  with  a  very  efficient  reflux  condenser  to  prevent 
the  hydrochloric  acid  evolved  from  carrying  off  any  benzal  chloride. 
As  the  dichlortoluene  used  is  generally  not  pure,  the  product  is 
distilled  in  vacuo.  At  16  mms.  about  i  %  dichlorbenzal  chloride 
comes  over  at  116-119°,  and  95  %  at  120-130°  ;  the  residue  consists 
of  resins  and  higher  chlorinated  products.  At  the  ordinary  pressure 
2:6- dichlorbenzal  chloride  boils  at  250°. 


100  gms. 
Dichlor- 
benzal 
chloride. 

200  gms. 
H2S04, 
66°  Be. 


(e)  Hydrolysis  of  2:6-Dichlorbenzal  Chloride. 

This  is  more  difficult  than  with  ordinary  benzal  chloride  ;  in 
contrast  to  this  latter  substance  it  cannot  be  hydrolysed  with  water 
and  iron,  or  with  lime  or  caustic  potash,  even  under  pressure  at  150°. 
It  is  possible,  however,  to  obtain  the  desired  aldehyde  by  means  of 
concentrated  sulphuric  acid,  although  a  considerable  portion 
becomes  resinified  whilst  so  doing. 

100  Gms.  2:6-dichlorbenzal  chloride  are  stirred  with  200  gms. 
66°  Be.  sulphuric  acid  at  55°  for  12,  hours.  The  solution  is  then 
poured  into  a  litre  of  water,  the  product  run  off  from  the  dilute 
sulphuric  acid,  and  distilled  in  steam.  Yield  about  30  gms.  pure 
2:6-dichlorbenzaldehyde.  M.p.  71°. 

Notes  on  Works  Technique  and  Practice. — 2:6-Dichlorbenzaldehyde 
has  become  a  fairly  important  intermediate  in  recent  years,  as  it  is 
the  starting-point  for  several  colours  of  the  Aurine  series  (Erio 
Chrome  Azurol,  etc.).  It  is  also  very  interesting  from  the  technical 
point  of  view,  as  it  is  produced  as  a  result  of  three  types  of  chlorina- 
tion. The  first  two  chlorinations  offer  no  difficulty  on  the  large 
scale,  but  the  third  is  by  no  means  easy  to  carry  out.  The  chief 
difficulty  is  the  unreliability  of  large  glass  vessels  ;  iron,  copper, 
tin,  etc.,  cannot  be  used,  and  enamel  cracks  at  such  high  tempera- 
tures. One  is  therefore  forced  to  carry  out  the  chlorination  in  a 
number  of  small  glass  carboys,  holding  10-15  litres,  which  are  heated 
on  sand-baths  by  means  of  gas  or  on  the  Frederking  system.  Owing 
to  the  frequent  breaking  of  the  glass  vessels,  steam  heating  offers  the 


OXIDATIONS  93 

best  protection  against  fire,  but  at  the  same  time  there  are  such  high 
pressures  (200  atm.)  in  the  steam  pipes  that  there  is  always  the 
possibility  of  explosions.  For  this  reason  the  simple  sand-bath  is 
usually  preferred.  Recently  attempts  have  been  made  to  facilitate 
the  introduction  of  chlorine  into  the  side  chain  by  the  use  of  ultra- 
violet rays  from  a  Uviol  lamp.  This  only  succeeds,  however,  when 
there  is  no  trace  of  iron  present  in  the  reaction  mixture.  Even  the 
minute  traces  of  iron  in  the  quartz  lamp,  or  in  the  porcelain  vessels, 
or  the  dust  of  the  factory  containing  iron  rust,  may  cause  serious 
disturbances.  The  temperature  should  be  low  at  first,  then  rising 
gradually  to  100°. 

The  preparation  of  2:6-dichlortoluene  is  one  of  the  few  technical 
examples  of  the,  application  of  Sandmeyer's  reaction  ;  so  far  as  I  am 
aware,  the  only  other  substance  made  by  this  method  is  2-chlor- 
benzaldehyde.  The  chlorine  atom  in  such  compounds  may  be 
easily  replaced  by  a  sulphonic  group  on  heating  to  150°  with  neutral 
sulphite.  Orthosulphonated  benzaldehydes  give  alkali-fast  tri- 
phenylmethane  colours  such  as  Patent  Blue,  Erio  Glaucine,  and 
Xylene  Blue. 

In  the  works  the  distillation  at  the  various  intermediate  stages 
is  not  performed  ;  but  the  dichlortoluene  must  be  distilled  to  obtain 
it  absolutely  dry. 

It  is  sufficient  to  separate  the  remaining  compounds  from  their 
mother-liquors  in  homogeneously  lead-lined  separating  funnels. 
The  copper  solutions  are  always  worked  up  again  for  cuprous 
chloride  by  means  of  zinc  dust,  the  loss  on  a  single  operation  rarely 
exceeding  2  %. 


4.   OXIDATIONS^ 

Dinitrostilbene-Disulphonic    Acid    and    Diaminostilbene- 
Disulphonic  Acid  from  />-Nitrotoluene. 

(Conjoint  oxidation  of  two  molecules.) 
Reaction  : 

CH3  CH3  CH 

HS03/N    ^    HSO/N 

NO2  NO2  NO2 

1  C/.  also  Malachite  Green  and  Xylene  Blue  VS. 


94 


INTERMEDIATE  PRODUCTS 

=CH 
HS03|  ^ 

N 

NH9  NH, 


100  gms.  p- 
Nitro  toluene. 
280-320  gtns. 


Ice. 


300  gms. 
H20. 
300  gms. 
250  gms. 
NaCl. 
50  gms. 
Soda. 
2  1.  Water. 
1 60  gms. 

NaO°H. 
1700  gms. 

5  % 
NaOCl 
(  =  85  gms. 
ioo  % 
NaOCl). 
300  gms. 
NaOH 
(35  %). 


400  gms. 
NaCl. 


(a)  Dinitrostilbene-Disulphonic  Acid. 

oo  Gms.  />-nitrotoluene  are  sulphonated  exactly  as  described  for 
nitrobenzene,  and  the  product  separated  as  the  sodium  salt.  The 
press-cakes  are  dissolved  in  500  c.cs.  of  water  at  60°  with  the  aid  of 
soda,  about  50  gms.  being  required  ;  if  more  be  needed,  the  cakes 
were  insufficiently  pressed.  The  solution  is  filtered  from  iron  oxide 
which  is  nearly  always  present,  and  made  up  to  2  litres  at  50°.  To 
the  well-stirred  liquid  160  gms.  of  35  %  caustic  soda  lye  are  added 
during  half  an  hour  ;  no  sodium  salt  of  the  sulphonic  acid  should 
separate  out.  A  mixture  of  1700  gms.  sodium  hypochlorite  solution 
containing  about  5  %  NaOCl,  and  300  gms.  of  35  %  caustic  soda  lye 
is  then  allowed  to  drop  in  similarly  during  10  hours.  The  strength 
of  the  hypochlorite  must  be  exactly  determined  by  titration.  It 
should  be  remembered  that  only  hypochlorite  solutions  containing 
at  least  5  %  excess  NaOH  will  keep,  which  is  of  special  importance 
as  regards  the  preparation  of  the  hypochlorite  solution.  The 
temperature  must  not  exceed  56°,  as  otherwise  yellow  dyes  of  the 
Mikado  series  are  formed. 

The  mixture  is  now  allowed  to  stand  at  55°  for  at  least  24  hours, 
taking  care  that  free  chlorine  (hypochlorite)  can  be  detected  during 
the  whole  period  with  the  aid  of  potassium  iodide-starch  paper. 
It  is  then  cooled  to  15°,  400  gms.  of  salt  are  added,  and  the  whole  is 
allowed  to  stand  for  a  day.  The  sodium  salt  of  dinitrostilbene- 
disulphonic  acid  separates  out  as  a  yellow  crystalline  precipitate 
which  is  filtered  and  washed  with  a  very  little  brine.  The  yield  of 
crude  salt  is  about  ioo  gms. 


(b)  Reduction  to  Diaminostilbene-Disulphonic  Acid. 

The  sparingly  soluble  sodium  salt  is  dissolved  in  300  c.cs.  hot 
water,  the  free  soda  being  neutralized  with  a  little  dilute  hydro- 
chloric acid.  This  solution  is  allowed  to  run  on  to  200  gms.  of  iron 
200  gms.  Fe.  turnings  (which  have  been  etched  by  means  of  20  c.cs.  of  40  %  acetic 
40  C%  '  acid),  during  half  an  hour.  The  reduction  proceeds  according  to 

Acetic  acid,      the  known  method  (see,  for  example,  p.  67). 


About 

300  c.cs. 

water. 

A  little  HC1. 


OXIDATIONS  95 

The  clear  solution  is  made  strongly  acid  to  Congo  with  hydro-  About 
chloric  acid,  whereupon  the    diaminostilbene-disulphonic  acid  is  15  gms. 
precipitated  in  small  yellowish- white  crystals.     It  is  filtered  off  after  About 
standing    for    10    hours    and    thoroughly  washed.      The  yield   of  100  gms. 
sulphonic  acid  for  each  100  gms.  p-nitrotoluene  is  about  75  gms.  of 
100  %  product.     In  distinction  from  the  analogously  constituted 
2i2'-benzidine  disulphonic  acid,  it  cannot  easily  be  diazotized  by  the 
indirect  method. 

Notes  on  Works  Technique  and  Practice. — The  method  for  the 
preparation  of  diaminostilbene-disulphonic  acid  described  here  was 
first  given  by  Green,  and,  with  the  lowering  of  the  price  of  chlorine, 
it  has  completely  displaced  Leonhardt's  method.  The  old  process 
consisted  in  reducing  Mikado  Yellow,  which  was  obtained  by  the 
action  of  concentrated  soda  lye  upon  />-nitrotoluene  sulphonic  acid. 
By  this  method,  however,  only  48  %  of  the  theoretical  yield  of 
diamino  acid  is  obtained  even  under  the  most  favourable  conditions, 
and  large  quantities  of  zinc  dust  or  ammonium  sulphide  are  required 
for  the  reduction.  Further,  all  the  caustic  soda  is  lost,  whilst  by 
Green's  process  caustic  lye,  chlorate  and  common  salt  can  be 
recovered.  Again  Green's  product  is  much  purer  ;  if  too  con- 
centrated solutions  have  not  been  used  it  contains  absolutely  no 
diamino-dibenzyl  disulphonic  acid,  which  weakens  Chrysophenin 
considerably.  The  presence  of  the  dibenzyl  derivative  can  be 
readily  detected  by  means  of  two  reactions  :  first,  the  dye  from 
H-acid  and  the  dibenzyl  acid  is  much  redder  than  that  from  the 
stilbene  derivative,  and  secondly,  the  "  Chrysophenin  "  from  the 
dibenzyl  derivative  turns  almost  reddish- violet  with  mineral  acids, 
and  not  a  pure  blue.  A  comparatively  small  content  of  diamino- 
dibenzyl  disulphonic  acid  can  be  recognized  at  once  by  comparison 
with  a  specimen  of  the  pure  colour.  -  The  oxidation  to  the  dinitro 
acid  is  carried  out  in  concrete  vats.  It  is  to  be  noted  that  a  very 
small  content  of  iron  or  even  of  copper  immediately  decomposes 
the  hypochlorite  solution,  wood  being  inadmissible  also  for  the  same 
reason. 

Anthraquinone  from  Anthracene. 
Reaction : 

CH  CO 


\/ 

CH  CO 

Anthracene.  Anthraquinone. 


300  gms. 
ioo  % 
Anthracene. 

600  gms. 
Na2Cr2O7. 
6  1.  H20. 
1800  gms. 
50% 
H2SO4. 


96  INTERMEDIATE  PRODUCTS 

The  anthracene  used  for  the  preparation  of  anthraquinone  should 
not  be  too  impure,  or  too  much  chromic  acid  will  be  used  up.  At 
the  present  day,  the  tar  distilleries  deliver  a  product  of  80-92  % 
purity,  which  is  estimated  by  the  recognized  methods  (cf.  Lunge, 
"  Untersuchungsmethoden  ").  The  commercial  product  is  crystal- 
lized from  pyridine. 

Before  oxidizing,  the  anthracene  must  always  be  sublimed  by 
means  of  superheated  steam  at  about  200°,  as  only  in  this  way  can 
it  be  reduced  to  a  sufficiently  fine  state  of  division  for  use. 

300  Gms.  moist  sublimed  anthracene,  calculated  as  ioo  %  product, 
are  stirred  up  with  6  litres  of  water  in  a  large  lead-lined  iron  vessel 
and  600  gms.  sodium  bichromate  are  dissolved  in  it  at  the  same  time. 
The  mixture  is  heated  to  80°  by  means  of  a  Fletcher  burner,  and 
1800  gms.  50  %  sulphuric  acid  are  run  in  from  a  dropping  funnel 
during  10  hours.  The  presence  of  chromic  acid  must  always  be 
clearly  shown,  and  the  mixture  must  be  stirred  by  means  of  a  glass 
or  wooden  stirrer  ;  finally,  the  mixture  is  boiled  up  for  2  hours, 
replacing  the  evaporated  water.  The  product  is  filtered  off  and 
thoroughly  washed.  The  mother-liquor  may  be  worked  up  for 
chrome  alum  or  for  chromic  sulphate.1 

The  thoroughly  dried  crude  anthraquinone  still  contains  some 
unchanged  anthracene  together  with  other  impurities,  and  is  carefully 
purified  before  working  up  further.  Most  of  the  impurities  are 
removed  by  partial  sulphonation,  the  pure  product  being  finally 
redistilled  with  superheated  steam. 

The  powdered  and  dried  crude  anthraquinone  is  heated  with 
two  and  a  half  times  its  weight  of  60°  Be.  sulphuric  acid  to  120°,  so 
long  as  sulphurous  acid  is  evolved.  After  about  3  hours  the  mixture 
is  poured  into  about  three  times  its  weight  of  water,  filtered  and 
thoroughly  washed.  The  purified  anthraquinone  is  then  sublimed 
with  steam  at  240-260°.  It  is  obtained  as  a  fine  faintly  yellow 
powder  (for  apparatus  see  Fig.  17).  The  yield  of  dried  product 
obtained  from  ioo  gms.  pure  anthracene  is  about  106  parts  of  sublimed 
ioo  %  anthraquinone. 

Notes  on  Works  Technique  and  Practice. — The  oxidation  of 
anthracene  is  carried  out  in  the  works  in  lead-lined  wooden  vessels, 
or  homogeneously  lead-lined  iron  vessels,  of  very  large  dimensions. 
Vats  holding  from  15-25  thousand  litres  are  by  no  means  rare. 
The  chromic  sulphate  which  is  formed  as  a  by-product  plays  an 


1  Careful  note  should  be  made  of  the  fact  that  commercial  sodium  bichromate 
nearly  always  has  its  CrO8  content  reduced  to  that  of  the  potassium  salt  by  means 
of  Glauber  salt. 


CONDENSATIONS  97 

important  part  in  calculating  the  cost  of  the  product,  as  it  finds  use 
for  the  chrome-tanning  of  leather. 

Attempts  to  obtain  anthraquinone  by  other  means,  such  as 
nitrous  oxides  and  air,  have  failed,  not  on  account  of  any  special 
technical  difficulties,  but  owing  to  purely  business  considerations. 
The  B.A.S.F.,  for  instance,  attempted  the  oxidation  of  anthracene 
with  N2O3  in  the  form  of  vapour,  but  had  to  go  back  to  the  old 
process  after  a  short  time,  as  their  leather  customers  had  to  be 
provided  with  chromic  sulphate  without  fail,  and  it  was  not  possible 
to  obtain  it  so  cheaply  by  any  other  method.  The  Fabrik  Griesheim 
Elektron  are  said  to  carry  out  the  new  method  with  success.  This 
process  might  also,  under  some  conditions,  be  of  importance,  as  it  is 
independent  of  the  use  of  foreign  chrome-iron  ore.  Should  the 
chrome  leather  tanning  be  displaced  by  the  newer  synthetic  tanning 
materials,  then  it  is  quite  certain  that  the  chromic  acid  method  would 
in  time  gradually  disappear. 

The  distillation  of  anthracene  and  anthraquinone  is  carried  out 
in  apparatus  very  similar  to  that  required  for  diphenylamine  (cf.  p.  99). 
The  vapours,  however,  are  condensed  in  large  chambers,  about 
3X3X5  metres,  by  spraying  in  cold  water.  The  bottom  of  the 
chamber  is  covered  with  fine  calico,  which  allows  the  water  to  run 
off,  but  retains  the  sublimate. 


5.  CONDENSATIONS 

Diphenylamine  from  Aniline  and  Aniline  Salt. 
Reaction  : 


NH< 


NH< 


Cl 

=     /~  \— NH— 
+  [NHJC1 

93  Gms.  aniline  and  93  gms.  aniline  hydrochloride  (aniline  salt)  93  gps- 
are  heated  for  20  hours  to  230°  in  an  enamelled  autoclave  fitted  Amlme- 
with  an  enamelled  thermometer  tube.     The  pressure  reaches  about  Aniline  'salt. 
6  atms.     If  no  enamelled  thermometer  tube  is  obtainable,  it  suffices 
simply  to  heat  up  to  the  requisite  pressure  and  to  note  the  external 
temperature  of  the  oil  bath,  which  is  about  25°  higher  than  the  actual 
internal  temperature.     After  2  hours,  the  water  present  is  cautiously 
blown  off  through  the  valve,  as  even  traces  have  a  very  unfavourable 

7 


98  INTERMEDIATE  PRODUCTS 

influence  on  the  reaction.  This  process  is  repeated  three  times 
during  the  course  of  an  hour,  a  certain  amount  of  aniline  and 
ammonia  also  escaping.  There  is  no  point  in  heating  for  longer  than 
20  hours,  as  the  only  effect  would  be  to  diminish  the  yield.  After 
cooling,  the  contents  of  the  autoclave  are  placed  in  a  porcelain  dish 
and  treated  with  a  litre  of  water.  The  whole  is  then  heated  up  to 
70  c.cs.  80°  and  70  c.cs.  of  30  %  hydrochloric  acid  are  added  until  just  acid 

30  %  HC1.  to  cong0  j  jt  is  then  allowed  to  cool  down  over-night.  The  crude 
diphenylamine  separates  out  as  a  solid  cake  which  can  be  easily 
separated  from  the  mother-liquor,  as  diphenylamine  does  not  form 
a  salt  with  the  dilute  hydrochloric  acid.  After  filtering  off,  it  is 
again  melted  up  with  a  little  water,  extracted  with  a  small  quantity 
of  hydrochloric  acid  and  washed  with  dilute  sodium  carbonate 
solution. 

The  diphenylamine  so  obtained  is  extremely  impure.  It  must 
therefore  be  distilled  with  superheated  steam.  For  this  purpose, 
it  is  placed  in  a  half-litre  distilling  vessel,  and  the  apparatus  put 
together  as  shown  in  Fig.  17.  The  oil-bath  is  heated  to  250°,  and 
the  superheater  is  then  started  up  with  an  ordinary  Fletcher  burner. 
The  water  must  be  carefully  removed  from  the  steam,  the  temperature 
of  the  superheated  steam  being  about  300°.  With  a  good  distillation 
it  is  easily  possible  to  get  over  half-part  base  for  each  part  water. 
The  diphenylamine  is  obtained  as  an  almost  colourless  liquid  which 
solidifies  to  pale  yellow  cakes.  By  pouring  into  water  it  is  obtained 
completely  pure  in  a  yield  of  about  100  gms.  ;  m.p.  55,°.  About 
55  gms.  aniline  can  be  recovered  from  the  acid  mother-liquors. 

Notes  on  Works  Technique  and  Practice. — The  autoclaves  employed 
must  be  enamelled  inside  the  cover  as  well  as  inside  the  vessel  itself. 
Traces  of  iron  or  copper  diminish  the  yield  of  diphenylamine  by 
3°~5°  %>  resinous  products  being  formed.  The  extraction  with 
hydrochloric  acid  is  effected  in  wooden  vats,  and  the  distillation  by 
means  of  superheated  steam  is  shown  in  Fig.  19.  For  superheating, 
modern  appliances  are  used  such  as  the  excellent  "  Heitzmann 
Superheater,"  etc.  It  is  possible  to  get  over  one  part  of  diphenyl- 
amine with  one  part  of  water  at  230°. 


/3-Naphthylamine  from  /3-Naphthol, 

Reaction  : 

/x     /\ 

.SO2H 


NH, 


CONDENSATIONS 


99 


C/5 

9 

2 
• 

DH 


I 

» 

w 

6 
fa 


IOO 


INTERMEDIATE  PRODUCTS 


144  gms. 
^-Naphthol. 
600  gms. 
(NH4)2S03 
(22  %). 
125  gms. 
20  %  NH3. 


no  gms. 
30  %  HC1. 
i !  litres  H2O. 


200  gms. 
Na2S04. 


On  heating  naphthol  with  ammonium  sulphite  the  sulphurous 
ester  of  naphthylamine  is  formed.  The  excess  of  ammonia  then 
immediately  converts  it  into  naphthylamine  and  ammonium  sulphite. 

144  Gms.  (i  mol.)  100  %  /3-naphthol  and  600  gms.  ammonium 
sulphite  are  heated  up  in  an  autoclave  provided  with  a  stirrer  and 
oil-bath.1  In  addition  125  gms.  of  20  %  ammonia  are  also  added. 
The  mixture  is  heated  for  8  hours  at  an  internal  temperature  of 
150°,  and  a  pressure  of  about  6  atms.  (N.B.  steel-tube  manometer). 
The  contents  are  then  allowed  to  cool,  and  the  resultant  cake  of 
/3-naphthylamine  is  broken  up  in  a  mortar,  after  which  the  mass  is 
thoroughly  washed  out  with  water  from  a  suction  filter.  The 
ammonium  sulphite  solution  may  be  used  several  times.  The  well- 
washed  base  is  dissolved  in  ij  litres  of  water  and  no  gms.  hydro- 
chloric acid — which  must  contain  no  sulphuric  acid — and  filtered 
warm,  a  certain  amount  of  naphthol  remaining  behind.  The  filtrate 
is  treated  with  a  solution  of  200  gms.  calcined  Glauber  salt  dissolved 
in  200  c.cs.  of  water,  the  naphthylamine  being  precipitated  as 
naphthylamine  sulphate.  It  is  then  allowed  to  stand  all  night,  the 
precipitate  being  then  filtered  off  and  well  washed  with  cold  water. 
For  many  purposes  the  dried  sulphate  is  used  directly  (cf.  p.  37). 

To  obtain  the  free  base  the  moist  sulphate  is  stirred  up  with  a 
litre  of  water  and  treated  with  60  gms.  calcined  soda  dissolved  in  a 
little  water.  Owing  to  the  sparing  solubility  of  the  sulphate,  the 
decomposition  takes  several  hours,  but  may  be  speeded  up  by  con- 
tinuous stirring  and  heating  to  8oc.  The  product  is  then  filtered  off, 
washed  and  dried  at  80°. 

Yield  about  130  gms.  dry  base,  or  85-95  %  of  theory. 

Notes  on  Works  Technique  and  Practice. — For  reactions  of  this 
type  it  is  absolutely  essential  to  use  autoclaves  fitted  with  an  oil-bath 
or  steam-jacket.  The  naphthylamine  separates  out  as  an  oily  layer 
at  the  bottom  of  the  reaction  vessel  so  that,  in  spite  of  stirring,  if  no 
oil-bath  be  used,  overheating  is  bound  to  occur,  leading  to  the 
conversion  of  a  considerable  portion  into  dinaphthylamine  and 
decomposition  products.  This  also  holds  good  for  the  preparation 
of  a-naphthol  (see  p.  102). 

For  technical  purposes,  the  /3-naphthylamine  is  usually  distilled 
in  vacuo,  but  great  care  must  be  taken,  as  it  easily  decomposes.  If 
the  base  is  not  isolated,  the  well-dried,  finely  powdered  sulphate 
mixed  with  i  %  of  soda  (cf.  also  Primuline)  is  added  to  the  sulphuric 
acid  or  oleum  as  the  case  may  be. 

1  Ammonium  sulphite  is  obtained  by  saturating  250  gms.  of  20  %  ammonia 
with  SO 2  and  then  mixing  the  ammonium  bisulphite  so  obtained  with  250  gms. 
ammonia. 


CONDENSATIONS  m    aoi 

Bucherer's  method  has  completely  displaced  the  older  way  of 
heating  naphthol  with  ammonia  as  this  gives  only  70  %  yields,  and 
requires  pressure  of  50-60  atms. 

The  Bucherer  reaction  may  also  be  used  for  other  substances, 
and  is  reversible.  For  example,  by  heating  H-acid  or  y-acid  with 
aniline,  sodium  bisulphite,  and  water  under  a  reflux  condenser,  the 
corresponding  phenylated  amino-naphthol  sulphonic  acids  are 
easily  obtained,  e.g. 

(a)  Phenyl-y-acid. 

Formula  : 

OH 


HO,S.e 


224  Gms.  100  %  y-acid,  750  gms.  sodium  bisulphite  (25  %  SO2),  224  gms. 
750  c.cs.  water  and  200  gms.  aniline  are  heated  under  a  reflux  for  y-acid- 
24   hours.     Sufficient  concentrated   sodium   carbonate   solution  is  25°%" 
then  added  to  give  a  distinctly  alkaline  reaction,  and  the  aniline  is  NaHSO3. 
distilled  off  with  steam.     On  acidifying  with  hydrochloric  acid  the  II°Q'CS' 
pure  phenyl-y-acid  is  precipitated.     Yield  about  90  %= :  270  gms.  200  gms. 
90  %  acid.  Aniline- 

(b)  Nevile  and  Winther's  acid. 
Reaction  : 

NH9  f  NH.SO.Hl  OH 

/\/i\ 

->     I        I 

\/\v 

S03H  {  S03H          J  SO3H 

Naphthionic  acid.  Naphthol  sulphonic  acid  1:4. 

Nevile  and  Winther. 

100  Gms.  of  100  %  naphthionate,  dissolved  in  200  c.cs.  of  water,  100  gms. 

are  boiled  for  a  day  under  a  reflux  with  600  gms.  of  sodium  bisulphite  ™ 

solution  (25  %  SO2).     Sufficient  30  %  caustic  soda  solution  is  then  acid, 

added  to  redden  thiazole  paper,  and  the  whole  is  boiled  so  long  as  soc?  c.cs. 

ammonia   is   evolved.     The   product   is   then   made   permanently  602ogms> 

mineral-acid  with  hydrochloric  acid,  the  crystalline  Nevile- Winther  25  % 

1ST    TTQ/^ 

acid  being  obtained  on  cooling  ;  it  is  separated  from  the  residual 
naphthionic  acid  by  redissolving  and  filtering.  Yield  up  to  80  %  of 
theory. 


102  INTERMEDIATE  PRODUCTS 

a-Naphthol  from  a-Naphthylamine. 
Reaction  : 

[NH3  "1  OH 

/N/N        S04H 

a-Naphthol. 

143  gms.  I43  Gms.  a-naphthylamine  are  mixed  with  no  gms.  66  %  Be. 

a-Naphthyl-    sulphuric  acid  and  i  litre  of  water,  and  the  whole  heated  to  200° 
at  14  atms.  pressure.     The  naphthylamine  should  first  be  melted 

H2°SO^,S'         in  the  hot  water  and  the  acid  then  added  in  a  thin  stream  with  good 

66^  Be.  stirring.     The  autoclave  should  be  either  lead-lined  or  enamelled 

2   '     and  provided  with  a  good  stirrer  ;  the  cover  may  be  made  of  iron,  as 

the  sulphuric  acid  is  not  volatile.     Here  also  it  is  necessary  that  the 

autoclave  should  be  oil-heated  in  order  to  prevent  any  overheating, 

otherwise,  especially  in  the  works,  the  lead  will  certainly  be  melted. 

After  8  hours  it  is  cooled  down  and  the  naphthol  separated  from 
the  mother-liquor,  the  ammonium  sulphate  being  recovered  from  the 
latter.  The  a-naphthol  is  melted  with  a  little  water,  and  after 
solidifying,  separated  from  the  liquid  ;  it  is  almost  chemically  pure. 
TO  obtain  it  absolutely  pure,  vacuum  distillation  is  resorted  to. 
Yield,  94-95  %  of  theory.  M.p.  94°. 

Notes  on  Works  Technique  and  Practice. — The  process  described 
above  is  the  cheapest  and  best.  There  is,  however,  another  which 
is  analogous  to  the  preparation  of  /3-naphthol.  The  sodium  salt  of 
a-naphthalene  sulphonic  acid  is  melted  with  caustic  soda  at  290-300°. 
The  sulphonation  is  carried  out  at  80-90°,  and  the  salting  out  effected 
in  as  concentrated  a  solution  as  possible.  Here  also  the  excess  of 
acid  may  be  removed  with  advantage  by  milk  of  lime  or  chalk,  after 
which  the  product  is  treated  with  soda,  and  the  evaporated  sodium 
salt  melted  up  without  further  treatment.  The  a-naphthol  so 
obtained  is  impure. 

Dimethylaniline. 

(Diethyl-  and  ethylbenzyl-aniline.) 
Reaction  : 
(a)  NH2  N(CH3)2 


Dimethylaniline. 


DIPHLEGMATING   COLUMNS. 


PLATE    IX. 


FIG.  25.  FIG.  25A. 

Kubierschky  Columns. 


FIG.  26. 
Raschig  Column. 


Diameter  of  columns,  50-150  cms.  Height,  8-16  cms.  The  upper  part  (1-2  metres)  is 
externally  cooled  during  rectification.  The  remainder  of  the  column  (7-15  metres) 
is  well  insulated,  and  the  top  opening  is  closed. 


CONDENSATIONS  103 

(b)  S09.C7H7 

I 
NH.C2H5  N.C2H5 


NH, 

Monoethylaniline.  p-Toluene-sulphonyl  deriva- 

tive of  monoethylaniline . 

N(C2H6)2 


Diethylaniline. 

For  the  preparation  of  dimethylaniline  an  iron  autoclave  is  used 
with  a  cast-iron  lining,  working  up  to  60  atms.  pressure  and  provided 
with  oil  bath,  manometer,  etc.  The  methyl  alcohol  (wood  spirit) 
used  for  the  alkylation  must  contain  no  traces  of  acetone  or  ethyl 
alcohol,  as  the  presence  of  such  impurities  leads  to  an  immense 
increase  in  the  pressure  ;  its  purity  must  therefore  be  tested  by 
means  of  the  iodoform  reaction. 

93  Cms.  of  pure  aniline  are  mixed  with  105  gms.  pure  methyl  93  gms. 
alcohol  and  9*4  gms.  of  94  %  (66°  Be.)  sulphuric  acid.    The  autoclave  Anilme- 
is  then  closed  and  the  oil-bath  heated  to  200°  ;  the  pressure  rises  to  CH-OH. 
about  30  atms.  and  the  contents  are  then  left  for  6  hours  at  215°.  9-4  gms. 
They  are  allowed  to  cool  and  are  then  treated  with  25  gms.  30  %  ^  ^' 
caustic  soda  lye.     In  order  to  split  up  the  sulpho-ammonium  bases  25  gms. 
formed  at  the  same  time  (which  are  only  decomposed  at  higher 
temperatures  into  sulphuric  acid,  alcohol  and  tertiary  amine),  the 
product  must  be  heated  up  to  170°  in  the  autoclave  for  a  further 
5  hours.1    The  contents  of  the  autoclave  are  distilled  over  with  steam, 
the  dimethylaniline  completely  salted  out  from  the  aqueous  solution 
with  common  salt,  after   which  it  is  removed  with  a  separating 
funnel  and  distilled  through  a  small  bulb  column.     It  is  obtained 
almost  chemically  pure  as  a  colourless  liquid  which  contains,  however, 
always  some  monomethylaniline.2     Yield  about  117  gms.     B.p.  192°. 

(b)  Diethylaniline. 

The  preparation  of  diethylaniline  in  the  laboratory  is  also  quite 
simple,  but  should  only  be  carried  out  in  enamelled  autoclaves,  as 
hydrochloric  acid  is  used  instead  of  sulphuric  acid,  ethyl  alcohol 

1  The  formation  of  quaternary  ammonium  bases  is  especially  noticeable  in  the 
preparation  of  ethylbenzyl-aniline  and  methylbenzyl-aniline. 

2  The  purity  may  be  tested  by  mixing  4  c.cs.  of  the  dimethylaniline  with  2 
c.cs.  of  acetic  anhydride.     The  temperature  should  not  rise  more  than  i°  at  most 
(acetic  anhydride  test). 


io4 


INTERMEDIATE  PRODUCTS 


130  gms. 
Aniline  salt. 

140  gms. 
Alcohol. 


no  gms. 

30% 

NaOH. 

40  gms. 
p-Toluene 
sulphonic 
chloride. 


being  simply  split  up  by  sulphuric  acid  into  water,  carbon,  and 
ethylene. 

130  Gms.  dried  aniline  hydrochloride  are  heated  with  140  gms. 
of  95  %  alcohol  to  180°  for  8  hours  in  an  enamelled  autoclave.  The 
pressure  rises  to  30  atms.  If  a  very  strong  autoclave  is  available,  the 
contents  may  be  heated  with  advantage  to  200°,  pressures  up  to 
55  atms.  being  produced.  After  cooling,  the  contents  of  the 
autoclave  are  placed  in  a  glass  bolthead,  the  alcohol  and  ethyl  ether 
distilled  off,  and  the  residual  mixture  of  mono-  and  diethylaniline 
treated  with  no  gms.  of  30  %  caustic  soda  solution.  This  product 
is  then  stirred  up  thoroughly  at  the  ordinary  temperature  with  about 
40  gms.  of  para- toluene  sulphonic  chloride.  By  this  means  the 
monoethylaniline  is  converted  into  the  toluene  sulphonic  derivative, 
which  is  not  volatile  in  steam,  so  that  the  diethylaniline  may  be 
distilled  over  quite  pure.  The  purity  is  tested  by  the  acetic  anhydride 
test,  the  sulphonic  chloride  treatment  being  repeated  if  necessary. 
Yield  about  120  gms. 

The  residual  toluene  sulphonic  derivative  may  be  hydrolysed 
with  concentrated  sulphuric  acid,  and  the  monoethylaniline 
recovered. 

Notes  on  Works  Technique  and  Practice. — The  heating  up  of  a 
big  autoclave  in  the  works  takes  from  4-6  hours,  and  must  be  carried 
out  very  cautiously.  As  soon  as  the  temperature  has  reached  about 
190°  the  pressure  rises  rapidly  by  itself  to  10-30  atms.  After  the 
reaction  is  finished,  the  excess  of  methyl  alcohol  is  blown  off,  together 
with  the  ether,  the  vapours  being  condensed.  The  hydrolysis  of  the 
sulpho-ammonium  base  is  carried  out  in  huge  boilers  containing 
from  3000-5000  kgs.  dimethylaniline. 

The  method  given  above  for  the  preparation  of  dimethyl-  and 
diethyl-aniline  is  not  very  satisfactory,  but  may  be  recommended  as  a 
simple  process.  A  cheaper  and  more  rational  method  of  preparation 
consists  in  using  less  alcohol  and  acid,  the  resultant  mixture  being 
saponified  directly  with  caustic  soda  lye.  The  monoalkyl  derivative 
is  then  converted  into  the  alkyl  benzyl  derivative  by  means  of  benzyl 
chloride  ;  this  process  is  effected  according  to  the  scheme  given  for 
the  preparation  of  Chrysophenin  and  nitrophenetole,  or  simply  by 
heating  the  monoalkyl  derivative  in  a  closed  vessel  at  125°  with  the 
necessary  quantities  of  benzyl  chloride  and  50  %  caustic  soda  lye  ; 
105  %  of  theory  of  benzyl  chloride  is  needed.  In  this  manner  it 
is  possible  to  arrange  to  obtain  any  required  quantity  of  dialkyl 
aniline  or  of  mixed  amine.  The  separation  is  effected  by  means  of 
steam  distillation,  the  non- volatile  benzyl  derivative  remaining 


CONDENSATIONS  105 

behind.  Complete  purification  is  effected  by  fractional  distillation 
in  vacuo  ;  only  absolutely  pure  products  give  the  best  yields  of  dyes 
of  the  Acid  Violet  or  Patent  Blue  series. 


Salicylic  Acid  from  Phenol. 
Reaction  : 


OH 


O.CO.OH  1  OH 


COOH 


Phenol.  Salicylic  acid. 

At  the  present  day  salicylic  acid  is  made  exclusively  by  the  Kolbe- 
Schmitt  method,  which  consists  in  treating  sodium  phenate  with  dry 
carbonic  acid  at  first  at  the  ordinary  temperature,  and  then  at  125° 
under  4-7  atms.  pressure.  The  preparation  is  practically  quantitative 
if  the  salt  is  absolutely  dry  and  very  finely  divided,  which  may  be 
attained  by  drying  and  grinding  the  substance  in  a  vacuum. 

93  Gms.  of  pure  phenol  are  placed  in  an  autoclave  provided  with  93  gms- 
a  valve  for  the  introduction  of  carbonic  acid  (Plates  I.  and  XIII.), 
together  with  i  gm.-molecule(4O'i  gms.  100%)  caustic  soda, free  from  40-1  gms. 
carbonate,  dissolved  in  100  gms.  water.1     The  solution  is  evaporated  ^aOH 
at  1 00°  with  continuous  stirring  under  reduced  pressure,  until  no 
more  water  comes  off.     The  dried  phenate  is  then  removed  from  the 
autoclave  and  powdered  as  rapidly  as  possible  in  a  previously  heated 
porcelain  basin.     In  order  to  protect  it  from  moisture  it  is  at  once 
reintroduced  into  the  autoclave  together  with  5—10  balls  of  about 
14  mms.  diameter  made  of  iron  or  stone,  which  serve  to  pulverize 
it  further  during  the  stirring  ;   the  mass  is  again  heated  to  165°  in 
vacuo  until  absolutely  dry,  which  requires  5-6  hours,  after  which  it 
is  cooled  down  to  30°,  and  then  carbon  dioxide  is  led  into    the 
apparatus  from  a  cylinder,  with  continuous  stirring.  .  By  means  of 
the  reducing  valve  on  the  cylinder,  the  pressure  is  regulated  so  that 
it  does  not  rise  higher  than  i  atm.     After  2  hours  the  pressure  is 
slowly  increased  to  5  atms.,  and  the  temperature  to  125°  ;    after  a 
further  hour  the  tube  is  disconnected  and  the  pressure  let  off.     When 
the  product  has  cooled  the  powdery  yellowish  salicylate  is  dissolved  400  c.cs. 
in  400  c.cs.  water  and  precipitated  with  125  gms.  hydrochloric  acid  H*°' 
(30  %).     The  salicylic  acid,  which  comes  out  in  a  practically  pure  HCI. 

1  The  caustic  soda  is  completely  freed  from  carbonate  by  dissolving  in  its  own 
weight  of  water  and  allowing  to  stand  for  a  day  at  50°.  The  solution,  after  filtering 
through  asbestos,  is  titrated,  using  phenolphthalein  as  indicator. 


io6  INTERMEDIATE  PRODUCTS 

form,  is  filtered  at  30°,  and  the  traces  of  phenol  washed  away  with  a 
little  water.  For  the  further  purification  it  may  either  be  distilled 
with  super-heated  steam  at  140°,  or  be  recrystallized  from  hot 
water,  after  precipitating  the  impurities  by  means  of  50  %  of  its 
weight  of  stannous  chloride.1 

The  yield  of  pure  distilled  salicylic  acid  is  125  gms.  from  93  gms. 
phenol. 

Notes  on  Works  Technique  and  Practice.  —  The  equipment  used 
in  the  works  is  modelled  on  the  laboratory  apparatus,  but  very 
powerful  stirring-gear  and  grinding  balk  are  used  from  the  start, 
so  as  to  make  it  unnecessary  to  remove  the  salt  from  the  autoclave 
for  powdering.  Special  stirring-gears  are  also  made  for  this  purpose 
with  interlacing  arms,  which  render  the  balls  superfluous.  To 
purify  the  salicylic  acid  it  may  be  sublimed  in  a  current  of  hot  air, 
a  beautiful  product  being  obtained  in  this  manner,  which  is,  however, 
not  quite  pure.  The  yield  of  colours  obtained  from  the  distilled  acid 
is  always  better.  The  process  is  almost  quantitative,  up  to  137  kilos 
salicylic  acid  being  obtained  from  93  kilos  phenol. 

In  a  similar  manner,  ortho-cresotinic  acid  is  obtained  from 
ortho-cresol.  In  this  case,  however,  the  operation  must  be  carried 
right  through  from  start  to  finish  without  interruption  as  the  sodium 
salt  of  ortho-cresol  is  spontaneously  inflammable.  About  20  %  of 
the  ortho-cresol  is  recovered  unchanged,  and  the  cresotinic  acid  must 
be  reprecipitated  from  water.2  In  spite  of  this,  however,  it  is  no 
more  expensive  than  salicylic  acid,  as  the  poor  yields  are  made  up  for 
by  the  cheapness  of  the  cresol. 

Gallamide  and  Gallic  Acid  from  Tannin. 

Reaction  : 

OH 

Gallicacia. 


(NH4)2S03+NH 

material. 


V 

CONH2 


1  D.  R.P.  65131  (1892). 

2  It  is  dissolved  in  soda,  the  boiling  solution  ptecipitated  with  hydrochloric 
acid,  and  the  liquid  filtered  hot. 


CONDENSATIONS  107 

The  most  important  raw  material  for  gallamide  and  gallic  acid 
are  Gall-nuts  and  Sumach  (Rhus  coriarid).  The  tannin  is  either 
hydrolysed  by  caustic  soda  into  sugar  and  gallic  acid,  or  by  the  action 
of  ammonium  sulphite  into  sugar,  gallic  acid  and  gallamide,  approxi- 
mately equal  parts  of  amide  and  acid  being  obtained. 

200  Gms.  tannin  together  with  200  c.cs.  water,  400  gms.  20  %  20°  gms 
ammonia,  and  100  gms.  sodium  bisulphite  solution  (25  %  SO2)  are  2QQ  gmg 
placed  in  a  soda-water  bottle  fitted  with  a  rubber  stopper,  which  is  H2O. 
then  heated  for  12  hours  in  a  water  bath  at  50°.     The  bottle  must  be  4°o  ' 
shaken  occasionally  to  ensure  complete  solution.    The  solution  is  then  I00 


concentrated  in  a  large  glass  flask  to  400  c.cs.  under  reduced  pressure.  25  % 

After  cooling,  sufficient  hydrochloric  acid  is  added  cautiously 
to  render  the  liquid  just  acid  to  litmus.  The  gallamide  is  com- 
pletely precipitated  within  24  hours.  (In  the  laboratory  it  is  fre- 
quently necessary  to  cool  down  a  small  portion  in  a  freezing  mixture, 
and  then  to  scratch  the  inside  of  the  vessel  in  order  to  start  the 
crystallization.) 

The  sparingly  soluble  gallamide  is  filtered  off  and  well  washed. 
The    mother-liquor   is   treated   with    100   gms.   of    30   %    caustic  ico^gms. 
soda  lye  and  the  ammonia  removed  in  vacuo.     The  liquid  is  then  3°  /0 
concentrated  again  to  300  c.cs.  and  acidified  with  sufficient  concen- 
trated hydrochloric  acid  to  turn  Congo  paper  just  blue.     The  sodium 
salt  of  gallic  acid  separates  out  in  the  course  of  a  few  days  in  the  form 
of  a  finely  crystalline  precipitate  which  is  filtered  off  and  pressed 
without  washing.     It  is  dissolved  in  100  c.cs.  water,  and  the  gallic 
acid  precipitated  from  the  solution  by  means  of  hydrochloric  acid. 
Yield  of  gallamide  and  gallic  acid  about  60  gms.  each. 

Notes  on  Works  Technique  and  Practice.  —  On  the  large  scale, 
solutions  of  tannin  are  used  which  are  obtained  by  extracting  the 
material  containing  the  tannin  with  hot  soft  water  on  the  counter- 
current  principle,  the  solutions  being  afterwards  evaporated  in  vacuo 
to  30°  Be.  The  process  is  carried  out  in  large  concrete  vats  which 
may  be  used  either  for  positive  or  negative  pressures.  The  crystal- 
lization of  the  gallamide  takes  from  10-14  days,  an<^  tnat  °f  tne  gaUate 
still  longer.  Tannin  solutions  ferment  readily,  so  that  it  is  necessary 
to  work  quickly,  particularly  during  the  summer  months.  The 
purity  of  the  gallamide  is  estimated  by  distilling  off  the  ammonia 
from  a  weighed  portion,  by  means  of  caustic  soda,  which  is  absorbed 
in  normal  hydrochloric  acid,  and  the  latter  titrated  back.  Good 
gallamide  should  be  92  %  pure. 

Gallamide  and  gallic  acid  are  used  in  large  quantities  for  the 
preparation  of  Oxazines  (see  Gallamine  Blue). 


II.  DYES 

6.  AZO  DYES 

As  the  azo  colours  form  at  the  present  day  by  far  the  largest 
group  of  synthetic  organic  colouring  matters,  I  have  prefaced  the 
sections  dealing  with  these  products  by  certain  general  methods, 
as  in  many  cases  the  diazotization  and  coupling  takes  place  according 
to  certain  well-defined  rules.  Exact  rules,  however,  cannot  be  laid 
down,  as  each  amine  and  each  phenol  has  its  own  peculiarities  which 
must  first  be  accurately  determined  by  experiment.  As  it  is  not 
possible  to  go  fully  into  details  in  this  book,  we  must  content  ourselves 
with  a  few  typical  examples.  The  methods  of  analysis  are  given  in 
the  analytical  portion. 


Diazotization  of  Amines. 

Aromatic  amines  are  diazotized,  usually  at  5-10°,  in  as  concen- 
trated a  solution  as  possible.  According  to  the  nature  of  the  amine 
a  greater  or  less  quantity  of  acid  is  used,  hydrochloric  acid  being 
nearly  always  taken  for  this  purpose,  as  sulphuric  or  nitric  acids  are 
only  of  use  in  exceptional  cases.  In  the  works,  however,  sulphuric 
acid  is  frequently  used,  owing  to  its  cheapness,  but  it  has  the 
disadvantage  that,  on  salting  out  the  finished  dye,  Glauber  salt 
crystallizes  out,  which  weakens  the  colour  and  may  even  make  it 
unfilterable. 

Aniline. 

(Toluidine  ;    Xylidine  ;    Meta-nitraniline.) 

9*3  Gms.  (i/io  mol.)  aniline  are  stirred  up  by  means  of  a  glass 
rod  with  30  c.cs.  hot  water  and  25  c.cs.  concentrated  hydrochloric 
acid  are  then  added  in  a  thin  stream.  The  solution  is  allowed  to 
cool  somewhat,  and  when  it  has  reached  40°  sufficient  ice  is  added  to 
bring  the  temperature  down  to  o°,  leaving  a  slight  excess  of  ice.  A 


AZO    DYES  109 

solution  of  7  gms.  100  %  sodium  nitrite  (20  %  solution) l  is  then 
added  rapidly  with  vigorous  stirring.  This  solution  of  nitrite  is 
best  kept  as  a  stock  solution  standardized  by  means  of  pure  sulphanilic 
acid.  The  diazotization  is  complete  as  soon  as  a  drop  of  the  dia- 
zonium  solution  reacts  with  potassium  iodide  paper  and  with  Congo 
paper.  Every  diazotization  should  be  followed  by  means  of  both  of 
these  reagents.  The  diazotization  occupies  about  2  minutes  (half 
an  hour  on  the  large  scale),  the  end-temperature  being  about  7°  and 
the  total  volume  about  250  c.cs. 

In  the  cases  of  p-toluidine  and  chloraniline  a  certain  amount  of 
the  hydrochloride  often  separates  out  during  the  ice-cooling,  but 
rapidly  disappears  during  the  diazotization. 

^-Nitraniline. 

(o-Nitraniline,  etc.) 

As  the  salts  of  />-nitraniline  are  unstable  in  aqueous  solution, 
the  base  must  be  brought  into  reaction  in  a  very  finely  divided 
condition. 

14*5  Gms.  (i/io  mol.)  commercial  nitraniline  are  dissolved  in 
30  c.cs.  concentrated  hydrochloric  acid  and  30  c.cs.  water  at  80-90°, 
and  the  clear  solution  is  then  allowed  to  flow  in  a  fine  stream  on  to 
50  c.cs.  of  water  and  50  gms.  of  finely  crushed  ice  with  good  stirring  ; 
final  temperature  about  80°.  7  Gms.  sodium  nitrite  as  20  %  solution 
are  then  run  in  with  vigorous  stirring  ;  the  temperature  rises  to 
15°,  and  the  solution  becomes  clear  in  a  few  seconds.  The  liquid 
is  tested  with  Congo-  and  nitrite-paper.  On  the  large  scale,  also, 
the  nitrite  must  be  run  in  very  rapidly  under  the  surface  of  the  liquid, 
as  otherwise  considerable  quantities  of  diazo-amino  compounds  are 
formed. 

a-Naphthylamine. 

14*3  Gms.  (i/io  mol.)  a-naphthylamine  are  dissolved  in  22  gms. 
30  %  hydrochloric  acid  and  100  c.cs.  hot  water,  and  the  solution  is 
then  cooled  down  to  o°  with  200  gms.  ice.  60  Gms.  salt  are  added, 
and,  as  soon  as  the  temperature  has  gone  down  to  -5°,  20  gms. 
20  %  sulphuric  acid,  and  then,  quickly,  7  gms.  100  %  sodium  nitrite 
as  20  %  solution.  The  diazotization  is  completed  in  a  few  minutes, 
the  sparingly  soluble  sulphate  of  naphthylamine  going  into  solution. 
The  final  volume  is  about  800  c.cs.  and  the  temperature  below  o°. 

1  Volume  per  cent.  :   i  litre  =  200  gms.  100  %  sodium  nitrite. 


no  DYES 

Sulphanilic  Acid. 

(Metanilic  Acid,  Naphthionic  Acid,  Nitraniline  Sulphonic  Acids,  Chloraniline 
Sulphonic  Acids,  Diamino-Stilbene  Disulphonic  Acid,  Primuline  Sul- 
phonic Acid,  etc.) 

17-3  Gms.  (i/io  mol.)  100  %  sulphanilic  acid  are  dissolved  in 
100  c.cs.  of  water  with  the  aid  of  5*5  gms.  soda.1  25  C.cs.  hydro- 
chloric acid  are  added  and  the  whole  diazotized  with  35  c.cs.  20  % 
sodium  nitrite  solution  with  good  stirring.  The  diazotization 
takes  about  10  minutes,  and  the  temperature  may  be  allowed  to 
reach  15°. 

Diazo  compounds  which  contain  a  sulphonic  group  are  usually 
sparingly  soluble  and  come  down  as  their  internal  anhydrides  in  the 
form  of  white  or  yellow  crystalline  precipitates.  As,  in  addition, 
many  amino  sulphonic  acids  are  also  sparingly  soluble,  it  is  necessary 
to  diazotize  them  indirectly.  For  this  purpose  the  sodium  salt  of 
the  sulphonic  acid  is  mixed  with  the  necessary  quantity  of  the 
sodium  nitrite  and  the  mixture  is  then  poured  into  the  acid. 

Further  difficulties  are  caused  by  the  fact  that  certain  amines 
couple  with  themselves,  for  instance,  Cleve  acid,  and  for  these  an 
excess  of  about  5  %  sodium  nitrite  is  necessary. 

Benzidine. 

(o-Tolidine,  o-Dianisidine.) 

18*6  Gms.  (i/io  mol.)  of  technically  pure  benzidine  are  dissolved 
in  23  c.cs.  of  30  %  hydrochloric  acid  and  100  c.cs.  water  at  yo0.2 
The  solution  is  cooled  to  30-40°  when  50  gms.  ice  are  added,  a 
portion  of  the  hydrochloride  being  precipitated.  A  further  23  c.cs. 
hydrochloric  acid,  diluted  with  a  little  water,  are  then  added  with 
good  stirring,  a  fresh  quantity  of  the  salt  coming  out.  70  C.cs.  of 
20  %  sodium  nitrite  solution  are  then  run  in  rapidly  within  10  seconds. 
The  temperature  is  about  10-12°,  and  the  solution  should  become 
clear  in  one  minute.  If  the  temperature  has  been  kept  too  low 
the  last  traces  of  benzidine  sulphate  may  remain  until  8  or  10  minutes 
have  elapsed.  The  solution  is  tested  in  the  usual  way  with  Congo- 
and  nitrite-papers  ;  it  is  practically  neutral,  but  no  diazo-amino 
compound  is  formed  in  this  case  as  with  aniline. 

1  Sulphonic  acids  which  are  already  in  the  form  of  their  salts  are,  of  course, 
merely  dissolved  in  water. 

2  To  obtain  quite  clear  solutions,  it  is  necessary  to  use  hydrochloric  acid  free 
from  sulphuric  acid. 


AZO    DYES  in 

Tolidine  and  dianisidine  must  not  be  boiled,  but  are  best 
dissolved  below  40°,  or  the  finely  divided  substance  is  stirred  up  to  a 
paste  with  water.  In  the  works  the  solutions,  together  with  half  the 
hydrochloric  acid,  are  allowed  to  stand  over- night,  the  ice  and 
remainder  of  the  hydrochloric  acid  being  added  next  day. 


The  Coupling  of  an  Azo  Component. 

Diazo  compounds  are  distinguished  as  strong  or  weak  coupling 
substances  according  to  whether  they  combine  with  salicylic  acid 
or  not.  In  many  cases  the  combination  may  be  brought  about  by 
the  use  of  a  large  excess  of  soda  or  caustic  soda  lye,  though  often 
even  this  expedient  'fails,  as  many  diazo  compounds,  indeed,  are 
decomposed  by  alkali  before  the  coupling  takes  place,  and  in  these 
cases  it  is  necessary  to  use  sodium  acetate  or  formate  to  combine 
with  the  mineral  acid  which  is  set  free.  Generally  speaking  it  may 
be  said  that  the  diazo  solution  must  be  run  into  the  phenol  or  amine  ; 
there  are  very  few  exceptions  to  this  rule. 

A  general  scheme  for  coupling  is  given  here  which  may,  in  many 
cases,  be  made  use  of  just  as  it  stands. 

i/io  gm. -molecule  phenol  (naphthol,  amino-naphthol  sulphonic 
acid,  etc.)  is  dissolved  in  15  c.cs.  of  30  %  caustic  soda  solution  and 
25  gms.  sodium  carbonate,  together  with  the  necessary  quantity  of 
water,  and  the  whole  cooled  with  ice  to  o°.  The  more  concentrated 
the  solution,  the  more  smoothly  will  the  coupling  take  place  ;  the 
more  acid  used  for  diazotizing,  the  more  alkali  will  be  necessary.1 
The  diazonium  solution  (diazo  compound)  is  allowed  to  run  in  a 
thin  stream  into  this  cold  solution,  the  whole  being  stirred  gently 
for  i  hour  at  a  low  temperature.  The  temperature  is  then  raised 
to  30°  in  the  course  of  an  hour,  the  liquid  is  allowed  to  stand 
over-night,  and  next  day  the  dye  is  separated  out  at  a  suitable 
temperature. 

The  conditions  necessary  for  separating  out  the  dye  are  very 
varied  :  it  may  either  be  filtered  off  in  the  cold  directly  after  coupling, 
or  it  may  be  heated  up  and  taken  into  solution,  and  then  reprecipitated 
either  by  salting  out  or  acidifying.  In  rare  cases  it  may  be  impossible 
to  separate  out  the  dye,  and  one  is  forced  to  evaporate  down  the 
whole  solution  to  dryness. 

In  the  case  of  amines  the  scheme  for  the  coupling  needs  modifica- 
tion in  that  the  base  is  dissolved  in  acid  (hydrochloric,  acetic,  or 

1  Very  strongly  acid  diazonium  solutions  are  neutralized  with  soda  before 
coupling. 


112 


DYES 


formic  acid),  and  the  alkali  is  replaced  by  acetate  or  formate.  In 
very  rare  cases  no  addition  is  necessary,  as  the  coupling  takes  place 
spontaneously  with  elimination  of  mineral  acid.  Certain  amines 
insoluble  in  water,  such  as  diphenylamine,  cresidine,  a-naphthyl- 


FIG.  21. — Calibrated  vessel  for  coupling. 

amine,    etc.,    are    sometimes    coupled    in    alcoholic    solution    (cf. 
Tropseolin). 

The  pot  illustrated  above  (Fig.  21)  is  specially  suited  for 
coupling.  The  rough  graduation  makes  it  easier  to  estimate  the 
quantity  of  fluid  present. 


PLATE   X. 


AZO    DYES  113 

EXAMPLES  OF  SIMPLE  ALKALINE  COUPLINGS. 

Acid  Orange  A  or  Orange  II, 

Formula  :  M       /     \  Qn  „ 

\  NS        \  >S°3H 

^—/ 


17"  3  Gms.  (i/io  mol.)  of  100  %  sulphanilic  acid  are  dissolved  in   17*3 
200  c.cs.  water  and  6  gms.  soda,  any  excess  of  aniline  present  being  ^j^ 
driven  off  with  steam  by  boiling.     After  filtering,  30  c.cs.  concen-  6  gms.  Soda. 
trated  hydrochloric  acid  are  added,  and  the  whole  cooled  down  to  200  c.cs. 
20°.     By  means  of  a  little  ice,  the  temperature  is  brought  down  to   302CCS  HC1 
10°,  and  the  liquid  is  then  diazotized  below  15°  with  7  gms.  100  %   (30  %). 
sodium  nitrite  until  a  permanent  reaction  is  given  with   nitrite-   j^mQ 
and  Congo-papers.  (100  %). 

At  the  same  time  14*2  gms.  (i/io  mol.)  /3-naphthol  are  dissolved   i4-2  gms. 
in  15  gms.  of  30  %  caustic  soda  solution,  25  gms.  soda,  and  200  c.cs.  £-NaPhtho!- 
water  ;    the  /3-naphthol  should  dissolve  to  a  clear  solution.     The  30  %* 
naphthol  solution  is  cooled  to  3°  with  ice,  and  the  suspension  of  NaOH. 
diazo  sulphanilic  acid  added  in  a  thin  stream,  the  temperature  being  NafcS3 
kept  below  8°.     After  the  lapse  of  i  hour,  the  dye  formed  is  heated  to  2oo  c.cs. 
boiling  in  a  porcelain  basin  over  a  bare  flame,  and  the  boiling  solution  HaO. 
is  treated  with   100  gms.   common  salt  added  by  degrees.     The 
precipitate,  which  never  goes  completely  into  solution,  now  separates 
out  completely,  and  can  easily  be  filtered  at  50°  on  a  large  suction 
funnel.     The  filter-cakes  are  squeezed  in  a  screw-press,  after  which 
they  are  dried  at  100°.     The  yield  is  about  50  gms.,  but  can  only  be 
determined  exactly  by  making  comparative  dyeing  tests. 

Notes  on  Works  Technique  and  Practice.  —  Owing  to  its  cheapness 
and  brilliant  shade,  Acid  Orange  A  is  one  of  the  most  widely  used 
monoazo  dyes.  In  the  works  the  coupling  is  carried  out  in  very  large 
pitch-pine  tubs  holding  15,000  and  more  litres,  or  in  concrete  vats 
lined  with  pieces  of  earthenware,  holding  up  to  40  cubic  metres.  The 
illustration  on  Plate  VII.  shows  the  general  works  arrangement  with 
the  diazotizing  and  coupling  tubs,  together  with  the  pressure  vessel 
(Montejus)  and  the  filter-press.  The  filtered  colour  is  not  pressed 
hydraulically,  but  is  blown  through  in  the  filter-press  with  com- 
pressed air  for  1-3  hours,  and  is  then  dried  directly  on  copper  trays. 
For  this  purpose  vacuum  drying  ovens  are  coming  more  and  more 
into  use,  as  they  not  only  facilitate  rapid  drying,  but  also  afford 

8 


DYES 


considerable    protection    to    the    dye.     The    calculations    for    this 
colouring  matter  are  given  in  detail  later  on  (q.v). 


34"i  gms. 

100  % 

H-acid. 
S'8  gms. 
Na2CO3. 
200  c.cs. 
H20at 
70°  C. 
17  gms. 
Ac2O. 


Acetyl-H-Acid  and  Amidonaphthol  Red  G, 

Formula  : 

CH3'CO-NH  OH 

/1\/8\__N          /        \ 

I  I  2~~  \  / 

HO3S— I^JxjteOgH    X- 

34' i  Gms.  (i/io  mol.)  of  100  %  H-acid  are  dissolved  in  200  c.cs. 

water  and  5*8  gms.  soda,  at  70°. 
To  this  is  added  within  about 
20  seconds,  17  gms.  acetic  anhy- 
dride with  vigorous  stirring,  by 
which  means  the  amino  group  of 
the  H-acid  is  completely  acetylated. 
The  completeness  of  the  acety- 
lation  is  determined  by  acidifying 
a  small  test  portion  of  the  solution 
with  hydrochloric  acid,  adding  a 
few  drops  sodium  nitrite  solution, 
and  then  mixing  with  an  alkaline 
solution  of  H-acid.  If  no  un- 
changed H-acid  is  present,  no 
coloration  will  be  produced,  as 
no  diazotizable  group  will  be 
available. 

This  compound  may  be  coupled 
with  various  diazo  components  to 
give  beautiful  azo  colours  which 
are  very  fast  to  light,  and  which 
possess  excellent  levelling  proper- 
ties ;  with  diazotized  aniline,  for 
instance,  the  important  Amino- 
naphthol  Red  G  is  formed.  As  the 
acetyl  group  is  somewhat  easily 
hydrolysed,  it  is  necessary  to  carry 
out  the  coupling  with  very  little 
soda,  and,  in  addition,  to  have  some  ammonia  present,  which  vola- 
tilizes when  the  finished  colour  is  dried,  without  altering  the  latter. 


FIG.  22. — Laboratory  vacuum  filter 
(Nutsch). 


AZO    DYES  115 

9*3  Gms.  aniline  (i/io  mol.)  are  diazotized  as  described,  and  the  g'3  gms. 
diazonium  solution  is  then  mixed  with  the  ice-cold  acetyl-H-acid,  to  Amlme- 
which  15  gms.  of  100  %  soda  has  previously  been  added.     After  Na2CO3. 
i  minute,  20  c.cs.  concentrated  ammonia  are  added,  drop  by  drop,  20  c.cs. 
and  the  mass  is  allowed  to  stand  for  12  hours,  after  which  the  dye 
is  salted  out  in  the  cold  with  20  %  of  salt,  calculated  upon  the  volume  2o  %  NaCl. 
of  the  liquid.     The  dye  is  filtered  off,  well  pressed  in  the  screw-press, 
and  is  dried  at  50°.     Yield  about  50  gms. 

By  the  use  of  amino-acetanilide  (cf.  p.  71),  the  beautiful  bluish 
Aminonaphthol  Red  6B  is  obtained,  which  is  even  faster  to  light  than 
the  G  brand. 

Notes  on  Works  Technique  and  Practice. — The  dyes  described 
have  largely  displaced  the  analogues  from  chromotropic  acid  (di- 
hydroxynaphthalene  disulphonic  acid  1:8:3:6),  owing  to  their  greater 
cheapness  and  fastness  to  light. 

It  is  of  interest  to  note  that  it  is  not  feasible  to  carry  out  the 
acetylation  on  the  works  in  wooden  vessels  ;  if  such  be  used,  par- 
ticularly with  pitch-pine,  the  shade  of  the  finished  product  is  nearly 
always  dull.  For  this  reason  the  acetylation  is  carried  out  in  enamel 
vessels  ;  in  practice,  also,  a  somewhat  smaller  proportion  of  acetic 
anhvdride  is  made  use  of. 


Acid  Anthracene  Red  G  and  Chromocitronine. 
Formulae  : 

>r-N  :  N-/\COOH 


HO.S—/ 

»         2 


Acid  Anthracene  Red  G  (A  .G  F.A  .)  .  Chromocitronine  (D  .H.)  . 

Benzidine  disulphonic  acid  is  so  sparingly  soluble  that  it  must  be 
diazotized  indirectly  ;  for  this  purpose  it  is  dissolved  in  sodium 
carbonate  or  caustic  soda  solution,  and  the  sodium  salt  mixed  with 
sodium  nitrite  is  run  into  the  acid. 

Acid  Anthracene  Red  G.—  32  Gms.  benzidine  disulphonic  acid  32  gms. 
(100  %)  are  dissolved  in  300  c.cs.  warm  water  and  n  gms.  soda,  and  BenJdine 
the  solution  is  then  mixed  with  14  gms.  sodium  nitrite  (100  %)  disulphonic 

Qr»ir1 


n6 


DYES 


300  c.cs. 

H2O. 

ii  gms. 

Na2C03. 

14  gms. 

ioo  % 

NaN02. 

60  c.cs. 

30?7o 

HC1. 

3°  gms. 

0-NaphthoL 

30  gms. 

30% 

NaOH. 

50  gms. 

Na,C03. 


32  gms. 
Salicylic  acid. 
80  gms. 
Soda. 


at  20°.  This  solution  is  allowed  to  run  into  a  mixture  of  60  c  cs. 
°f  3°  %  hydrochloric  acid,  200  c.cs.  water,  and  ioo  gms.  ice  ;  the 
temperature  may  be  allowed  to  rise  to  25°  without  danger.  The 
diazotization  is  complete  in  a  few  minutes.  The  tetrazo  compound 
is  added  to  30  gms.  /3-naphthol  dissolved  in  exactly  the  same  pro- 
portions of  water,  caustic  soda,  sodium  carbonate  and  ice,  as  given 
under  Acid  Orange  A.  The  further  working  up  is  also  carried  out 
as  given  under  Acid  Orange.  It  may,  however,  happen  that  the 
tetrazo  benzidine  disulphonic  acid  separates  out  as  a  sparingly 
soluble,  coarsely  crystalline  precipitate  which  will  not  couple  with 
the  alkaline  naphthol  solution.  In  this  case  it  is  necessary  to  treat 
the  tetrazo  compound  at  o°  with  sufficient  caustic  soda  solution  to 
form  the  soluble  sodium  diazotate  ;  this  couples  instantaneously  with 
the  /3-naphthol.  Acid  Anthracene  Red  G  is  fast  to  milling  on  wool 
without  the  use  of  mordants. 

Chromocitronine.  (D.H.). — The  tetrazo  solution  of  the  benzidine 
disulphonic  acid  is  added  to  a  solution  of  32  gms.  pure  salicylic  acid 
dissolved  in  80  gms.  sodium  carbonate  and  200  c.cs.  water  at  5°. 
After  12  hours  the  dye  which  is  formed  is  salted  out  in  the  cold 
with  20  %  of  common  salt,  after  which  it  is  well  pressed  and  dried 
at  60°. 

In  this  case  it  is  unnecessary  to  redissolve  any  of  the  tetrazo 
compound  which  may  separate  out  under  certain  conditions  as  the 
Chromocitronine  itself  goes  into  solution  at  once.  It  is,  however, 
very  desirable,  especially  on  a  large  scale,  to  filter  the  solution  of  the 
finished  colour  before  salting  out,  in  order  that  the  printing  rollers 
may  not  become  smeared  when  it  is  used  for  calico  printing,  in  which 
it  finds  extensive  application.  The  wooden  tubs  always  splinter  off 
to  a  certain  extent,  which  is  liable  to  cause  a  good  deal  of  trouble  to 
the  printer.  Chromocitronine  is  a  beautiful  yellow  dye,  the  chrome 
lakes  of  which  are  distinguished  by  their  fastness  to  light,  washing, 
and  chlorine.  Owing  to  its  great  solubility  it  penetrates  well  into 
the  material  so  that  thin  fabrics  appear  to  be  printed  on  both  sides. 


Bismarck  Brown  G  and  R. 
Formulae  : 

NH2  NH2 

0— N  :  N— /\— N  :  N— 

Bismarck  Brown  G. 


AZO  DYES  ir 

NH2 


Bismarck  Brown  R. 

These  dyes  are  mixtures  of  various  colouring  matters,  in  which, 
however,  the  products  indicated  above  greatly  predominate.  The 
recipes  given  in  the  literature  on  the  subject  are  not  very  satisfactory, 
as  they  always  describe  the  treatment  of  an  acid  diamine  solution 
with  sodium  nitrite.  It  is,  however,  far  better  to  acidify  cautiously 
the  neutral,  mixed  solution  of  the  diamine  and  nitrite,  or  to  allow  the 
neutral  mixture  to  run  into  the  requisite  quantity  of  hydrochloric 
acid  during  12  minutes  ;  the  former  method  will  be  described  here. 
Somewhat  more  nitrite  is  required  than  corresponds  to  the  equation  : 

3  Diamine+2NaNO2+4HCl  =  i  Dye+(2HCl)+2NaCl. 

In  the  case  of  m-phenylene  diamine  the  excess  is  about  24  % ,  and  in 
the  case  of  toluylene  diamine  about  20  %,  i.e.  one  uses  for  3  mols. 
diamine,  2  mols.  nitrite -f- 20  %  or  24  %  excess,  respectively.  During 
the  formation  of  the  dye  the  diamine  base  disappears  completely  in 
both  cases,  as  may  be  seen  by  salting  out  a  test  portion. 

Bismarck  Brown  R  (Vesuvine  R,  etc.). 

36*6  Gms.  pure  toluylene  diamine  are  dissolved  in  i  litre  of  water  36-6  gms 
at  40°,  and  after  cooling  the  solution  is  mixed  with  i6'5  gms.  100  %   S^ine71 
sodium  nitrite.     The  volume  is  then  made  up  to  1600  c.cs.  with  ice   16-5  gms 
and  a  mixture  of  60  gms.  strong  hydrochloric  acid  and  60  c.cs.  water  NaNO2. 
is  then  run  in  under  the  surface  of  the  liquid  with  continuous  stirring  H,°O.C  °S 
during  20  minutes.     The  solution  becomes  deep  brown  at  once  and   120  gms. 
evolves  a  fair  amount  of  nitrogen.     The  end  temperature  is  about  10°.  ^-J0 
After  8  hours,  the  product  is  salted  out,  with  300  gms.  salt,  and  after  300  gms. 
standing  for  3  hours  the  mass  is  filtered,  the  extremely  soluble  dye  NaC1- 
being  washed  on  the  filter  with  its  mother-liquor.      It  is  dried  at  a 
low  temperature   (in  the  works  in  vacuo),  the  dry  product  weighing 
about  50  gms. 

The  dyeings  upon  tannined  cotton  are  fast  to  washing,  cheap,  and 
strong,  but  are  not  fast  to  light.  In  spite  of  this,  however,  both 
brands  of  Brown  are  much  used  for  cotton  and  silk,  and  especially 
for  leather.  Mixed  dyeings  with  Azo  Yellow  afford  good  brown 
shades  upon  upholstery  leather,  which  are  fast  to  light  and  rubbing. 


i8'6  gms. 

Tetrazotized 

benzidine. 

15  gms. 

Salicylic 

acid. 

40  gms. 

Na2C03. 


n8  DYES 

The  G  mark  is  made  in  a  precisely  similar  manner,  but  usually  it 
does  not  come  out  in  a  good  crystalline  form,  and  is  therefore  trouble- 
some to  filter  ;  this  disadvantage  can  be  removed  to  a  certain  extent 
by  using  a  larger  excess  of  nitrite. 


Benzidine  Colours. 

Benzidine  may  be  combined  with  all  the  phenols  and  amines 
which  are  used  for  the  production  of  azo  colours.  It  has  been  found 
that  only  one  of  the  two  azo  groups  of  tetrazo-benzidine  reacts 
vigorously,  the  other  being  relatively  inert.  In  this  way  it  is  possible 
to  prepare  not  only  benzidine  colours  which  have  a  single  phenol 
or  amino  component,  but  also  in  many  cases  the  so-called  "  mixed  " 
benzidine  dyes.  Such  products,  however,  are  only  formed  if  the 
first  dye  component  does  not  react  too  readily,  as  otherwise  some  of 
the  disazo  dye  will  be  formed  in  addition  to  the  intermediate  com- 
pound : 


HO-N=N-< 


-N=N-X 


It  would  take  far  too  long  to  mention  even  the  most  important  types 
of  such  intermediate  products,  so  that  we  must  therefore  confine 
ourselves  to  a  few  typical  examples.  Of  particular  importance  is  the 
intermediate  compound  which  is  formed  by  the  combination  of  a 
single  equivalent  of  salicylic  acid  with  benzidine.  This  is  formed 
very  simply,  as  a  second  salicylic  group  can  only  be  introduced  with 
difficulty  after  the  sodium  carbonate  coupling  by  means  of  an  excess 
of  caustic  soda  solution.  Further,  it  is  possible  to  couple  benzidine 
once  with  the  monoazo  dye  ^-nitraniline->H-acid,  or  with  H-acid 
alone  in  mineral  acid  solution  without  difficulty.  Both  cases  are 
discussed  in  detail  below. 


The  Intermediate  Compound  of  Benzidine  with  Salicylic 

Acid. 

(o-Tolidine  ->  o-Cresotinic  Acid.) * 

1 8* 6  Gms.  (i/io  mol.)  commercial  benzidine  are  tetrazotized  as 
described  on  p.  no.  The  clear  tetrazo  solution  is  poured  rapidly 
into  a  solution  of  15  gms.  pure  salicylic  acid  and  40  gms.  anhydrous 
sodium  carbonate,  and  300  c.cs.  water  at  5°.  The  orange-yellow 

1  The  compound  o-tolidine  ->  o-cresotinic  acid  is  largely  made,  whereas  salicylic 
acid  cannot  be  used,  as  the  dyes  from  o-tolidine  — >  salicylic  acid  are  very  sparingly 
soluble. 


AZO   DYES  119 

intermediate  compound  separates  out,  and  the  end  of  the  reaction 
may  be  recognized  by  placing  a  drop  on  filter-paper  and  testing  the 
colourless  rim  of  liquid  with  alkaline  H-acid,  when  no  blue  colora- 
tion should  be  given.  Stirring  is  continued  steadily  until  the 
benzidine  reaction  has  quite  disappeared,  which  will  take  about  i 
hour  at  12°. 

The  azo  compound,  which  has  the  formula  : 

COOH 
/ 
HO.N2-/~~V-/~   VN2-/~   \OH 

\  -  /  \  S  N^__/ 

can  combine  with  numerous  amines  and  phenols.  Certain  of  the 
dyes  produced  are  important.  On  adding  to  the  intermediate 
product,  for  example,  a  solution  of  y-acid  made  alkaline  with  sodium 
carbonate,  Diamine  Brown  V  (Cassella)  is  formed.  It  is  of  interest 
to  note  that  only  85  %  of  theory  of  y-acid  is  required.  If,  on  the 
other  hand,  the  intermediate  compound  is  acidified  with  acetic  acid, 
and  is  then  treated  with  a  solution  of  y-acid  which  is  still  distinctly 
acid  to  litmus,  the  important  Diamine  Fast  Red  F  is  formed  in 
about  12  hours  (at  12-28°),  which,  owing  to  the  presence  of  the 
salicylic  acid  group,  affords  chrome  mordanted  dyeings  on  wool 
which  are  fast  to  milling. 

Formula  of  Diamine  Brown  V  : 

,N2  —  Salicylic  acid 
Benzidine/  OH 


Formula  of  Diamine  Fast  Red  F  : 

'N2  —  Salicylic  acid 
Benzidme/ 


In  alkaline  couplings  the  azo  group  takes  up  the  ortho  position 
to  the  hydroxyl  group,  whilst  in  acetic  acid  coupling  the  ortho 
position  to  the  amino  group  is  attacked. 


I2O 


DYES 


Formula  : 


Dianil  Brown  3GN. 
COOH 


_ 

NH 


This  dye  is  one  of  the  most  frequently  used  direct  azo  colours, 
as  it  is  extraordinarily  strong.  It  is,  however,  not  fast  to  acids  or 
light.  First  of  all  the  monoazo  dye  Sulphochrysoidine  G : 


i/io  mol. 
Diazotized 
sulphanilic 
acid. . 

io'8  gms. 
w-Phenylene 
diamine. 
5  c.cs.  HC1. 


About  6 
gms.  Soda. 

About  5*5 
gms.  Soda. 
10  gms. 
Soda. 


H2N 

is  prepared  in  the  following  manner  :  17*3  gms.  (i/io  mol.)  sul- 
phanilic  acid  are  diazotized  as  already  described  (cf.  p.  113),  and  the 
suspension  of  the  diazo  compound,  which  must  be  slightly  mineral 
acid,  is  allowed  to  drop  slowly  into  a  solution  of  lO'S  gms.  purest 
m-phenylene  diamine.  Preferably  the  diamine  is  acidified  with 
5  c.cs.  concentrated  hydrochloric  acid  and  the  solution  made  up  to 
10  %  diamine.  The  coupling  is  followed  by  means  of  alkaline 
H-acid  solution  "  spotted  "  upon  a  filter-paper,  and  the  diazo  com- 
pound is  added  until  a  very  faint  red  colour  can  be  detected  on  the 
rim.  The  diamine  base  disappears  completely,  but  the  true  azo 
colour  is  not  yet  formed.  After  standing  for  2  hours  at  5°,  a  10  % 
soda  solution  is  run  in  cautiously  with  continuous  stirring,  until  the 
mineral  acid  has  been  fully  neutralized,  about  6  gms.  soda  being 
required  for  this  purpose.  After  standing  a  further  3  hours  at  5°, 
5*5  gms.  soda  are  added  during  i  hour,  and  the  whole  allowed  to 
stand  over-night.  Next  morning  a  further  10  gms.  of  sodium 
carbonate  dissolved  in  a  little  water,  are  added,  and  the  whole  again 
allowed  to  stand  for  3  hours.  It  is  most  essential  to  effect  the 
coupling  of  the  sulphanilic  acid  and  the  diamine  extremely  carefully, 
or  else  the  final  colour  will  be  weak.  The  sodium  salt  of  the  Sulpho- 
chrysoidine separates  out  for  the  most  part  as  a  reddish-brown, 
beautifully  crystalline  precipitate.  The  volume  of  the  whole  solution 


AZO   DYES  121 

may  be  about  500  c.cs.,  but  should  not  be  too  dilute.     This  suspension 
is  mixed    at    10°    with   the   intermediate    compound   benzidine  -> 
salicylic  acid  (cf.  p.  118),  and  the  mixture  stirred  steadily  for  5  hours,   i/io  mpl. 
It  is  then  warmed  cautiously  to  30°  and  allowed  to  stand  for  12  hours,  s&cylic  add. 


The  liquid  is  then  boiled  up  and  the  dye  salted  out  with  200  gms.  200  gms. 
common  salt.     It  should  be  a  pure  brownish  red,  and  should  be  NaC1- 
precipitated  in  an  easily  filterable  condition  ;    the  mother-liquor 
only  contains  very  little  Sulphochrysoidine.     The  yield  of  dry  colour 
is  about  95  gms.     It  will  only  dye  cotton  evenly,  however,  if  it  is 
mixed  with  10  %  of  its  weight  of  dehydrated  sodium  carbonate  ; 
too  little  or  too  much  soda  has  an  unfavourable  influence,  so  that  we 
have  here  a  case  similar  to  that  of  Direct  Deep  Black  EW  (cf.  p.  1  18). 

Notes  on  Works  Practice.  —  By  the  use  of  1:2:4  toluylene  diamine 
instead  of  m-phenylene  diamine  an  analogous  dye  is  obtained  which 
is,  however,  somewhat  faster  to  acids.  As  in  this  case  the  para 
position  to  the  amino  group  is  occupied,  it  follows  that  the  formula 
given  above  for  the  w-phenylene  diamine  colour  is  correct,  i.e.  the 
second  azo  group  is  attached  between  the  two  amino  groups  and  not 
in  the  position  para  to  the  NH2. 

If  the  diamine  is  first  coupled  with  the  benzidine-salicylic  acid 
compound  and  then  with  the  sulphanilic  acid,  an  isomeric  dye  is 
produced  of  the  following  formula,  which,  curiously  enough,  however, 
is  quite  valueless  : 

COOH 


It  is  very  important  to  use  quite  pure  diamine,  as  traces  of  o- 
or  />-diamine  decompose  a  large  portion  of  the  diazo-sulphanilic 
acid,  and  also  of  the  intermediate  compound,  benzidine-salicylic 
acid.  The  solution  foams  up  and  the  dye  becomes  weak  and  muddy. 
By  the  use  of  the  purest  materials  the  yield  is  increased  by  about 
40  %,  as  compared  with  the  impure  commercial  diamine  solution. 

The  colouring  matters  from  both  phenylene  and  toluylene  dia- 
mines  are  used  in  large  quantities  for  the  production  of  mixed  shades. 


122 


DYES 


14-5  gms. 
Diazotized 
p-ni  tramline, 
34' i  gms. 
TOO  % 
H-acid. 

200  C.CS. 

H2O. 

5  gms- 
Na2C03. 

20  gms. 
30  % 
NaOH. 

40  gms. 
Na2CO3. 


200  gms. 
NaCl. 


40  gms. 
Na2C03. 
9-3  gms. 
Diazotized 
aniline. 


Diamine  Green  B  (Cassella), 

Formula  :  OH  NH2 

/\     /\ 

-Nr 


OH 


14*5  Gms.  pure  ^-nitraniline  are  diazotized  as  described  on  p.  109, 
and  to  the  clear,  ice-cold  diazonium  solutioti  is  added  34' i  gms. 
100  %  H-acid  dissolved  in  200  c.cs.  of  cold  water  and  5-5  gms. 
sodium  carbonate.  The  addition  will  occupy  about  three-quarters  of 
an  hour,  and  care  must  be  taken  by  means  of  good  mechanical 
stirring  that  no  lumps  are  formed.  The  H-acid  combines  with  the 
nitraniline  in  4-5  hours,  setting  free  an  equivalent  portion  of  hydro- 
chloric acid.  The  mixture  is  now  allowed  to  stand  for  at  least 
12  hours,  and  next  day,  after  heating  up  to  50°,  20  gms.  of  30  % 
caustic  soda  solution  are  added  and  40  gms.  soda.  The  monoazo 
dye  of  the  formula  : 

OH  NH2 


NO, 


goes  into  solution  with  a  fine  blue  colour,  and  is  then  salted  out  by 
means  of  200  gms.  common  salt.  After  a  few  hours,  the  glistening 
sodium  salt  separates  out  in  an  easily  filterable  form,  after  which  it 
is  filtered  off  and  pressed.  The  mother-liquor  has  a  strong  blue 
colour,  but  does  not  yield  any  further  quantity  of  usable  dye  on 
saturating  with  common  salt  and  is  therefore  thrown  away. 

If  instead  of  separating  out  the  dye  from  />-nitraniline  this  is 
coupled  with  a  calculated  quantity  of  diazotized  aniline  at  5°,  the 
important  Naphthol  Blue-Black  B  (C.)  is  obtained,  having  the 
structure  : 

OH  NH2 

X"  -\_N2_/Y\ ,-N2-<~  ~>02 
H03sl     1     /'S03H 


AZO   DYES  123 

In  this  case  it  is  unnecessary  to  isolate  the  monoazo  dye,  but  an 
excess  of  diazotized  aniline  has  a  deleterious  influence.     By  salting 
out  at  90°  with  15  %  of  common  salt,  the  Naphthol  Blue-Black  B  is 
obtained  in  a  fine  bronzed  form.     In  passing,  it  may  be  mentioned  50  gms. 
that  by  reducing  Naphthol  Blue-Black  B  with  sodium  sulphide  at  Na2S.9H2O 
25°,  a  valuable  dark  green  azo  dye  is  obtained,  Azo  Dark  Green, 
having  the  following  formula  : 


NH< 


The  dye  is  precipitated  out  at  50°  after  standing  for  3  hours, 
with  15  %  of  common  salt  and  a  little  sulphuric  acid.  It  is  sparingly 
soluble  in  bicarbonate  ;  the  mother-liquor  is  deeply  coloured. 

The  following  general  rule  may  be  noted  :  Dyes  from  para- 
nitraniline  may  be  reduced  almost  quantitatively  to  the  corresponding 
/>-phenylene  diamine  azo  colours  by  means  of  the  calculated  quantity 
of  sodium  sulphide  : 

+Na2S  / — \ 

X— NrHf       ^N0      V    X-N-  NH2 


In  this  way  new  amino-azo  dyes  are  obtained  which  may  be  again 
diazotized  and  coupled  up  with  other  components.  The  same 
amino-azo  dyes  may  also  be  obtained  by  hydrolysis  of  the  corre- 
sponding />-amino-acetanilide  colours.1 

/— x  NaOH  /— \ 

X— N2— /     \NH.CO.CH3         -->    X— N2—/     \ 

85  ^ — * 

The  sodium  salt  is  dissolved  in  500  c.cs.  water  containing  40  gms.  500  c.cs. 
soda  at  80°,  and  is  then  allowed  to  cool  down  to  20°  with  continuous  H2°- 
stirring.     Sufficient  ice  is   then  added  to   bring  the  temperature 
down  to  4°  ;   a  portion  of  the  dye  separates  out  again  in  a  fine  state 
of  division.     To  this  suspension  is  added  slowly  a  solution  of  tetrazo-  About 
benzidine  prepared  as  described  on  p.  no,  the  solution  being  added  l8'6  &• . 
until  a  drop  on  filter  paper  gives  a  weak  but  distinct  blue  coloration  benzidine. 
on  touching  the  rim  with  alkaline  H-acid  solution.    At  first  the 
discoloration  always  fades  away  again,  so  that  a  further  quantity  of 
the  tetrazo  solution  must  be  added.     Altogether  about  i8'6  gms. 

1  Formyl-  and  oxalyl-/>-phenylene  diamines  may  also  be  utilized. 


124 


DYES 


benzidine  must  be  used,  the  formation  of  the  intermediate  compound 
taking  half  an  hour. 

Formula  of  the  intermediate  compound  : 


OH  NH2 

Benzidine(HO3S\    J\  /SO3H      N— 


NO, 


12  gms. 
Phenol. 


About 

40  gms. 

30% 

NaOH. 

150  gms. 

NaCl. 

About 

50  gms. 

50% 

H2S04. 

300  gms. 
NaCl. 


12  Gms.  of  phenol  melted  up  with  a  little  water  are  added  to  this 
compound  and  left  for  3  hours  at  10°,  after  which  the  temperature  is 
slowly  raised  to  30°,  and  the  mixture  allowed  to  stand  over-night. 
It  is  then  heated  up  to  60°,  and  sufficient  30  %  caustic  soda-lye  added 
to  bring  everything  into  solution  (about  40  gms  .)  .  1  150  Gms  .  common 
salt  are  now  added,  and  dilute  sulphuric  acid  dropped  in  cautiously 
until  the  colouring  matter  is  precipitated  (test  by  spotting  on  filter 
paper)  ;  the  latter  is  filtered  off,  pressed,  and  dried  at  90°.  Yield 
about  no  gms.  strong  dye.  Instead  of  using  caustic  soda  for  the 
separation  the  product  may  be  heated  up  to  90°  and  salted  out  hot 
with  300  gms.  common  salt.  The  product  is  not,  however,  so 
strong. 

Notes  on  Works  Technique  and  Practice.  —  In  spite  of  its  relatively 
poor  fastness  to  light,  Diamine  Green  B  is  one  of  the  most  largely 
used  green  cotton  dyes.  It  serves  for  dyeing  the  cotton  layer  used 
for  insulating  the  copper  wires  for  telephone  and  other  cables,  and 
for  the  production  of  mixed  shades.-  If  salicylic  acid  be  used  in 
place  of  the  phenol,  this  must  be  coupled  first  of  all,  as  it  does  not 
combine  readily  with  benzidine  when  used  as  a  second  component. 
The  product  so  obtained  is  Diamine  Green  G,  which  is,  however, 
much  less  used  as  the  formation  of  this  colour  does  not  take  place 
so  smoothly  and,  in  consequence,  the  price  is  considerably  higher. 
In  the  works,  the  heating  is  always  effected  by  blowing  in  steam,  and 
these  dyes  cannot  be  pressed  as  they  are  simply  forced  through  the 
filter-cloths. 


1  Nitro-azo  dyes  must  not  be  treated  with  soda-lye  in  presence  of  wood  or 
other  reducing  substances. 


AZO   DYES  125 

EXAMPLE  OF  THE  COMBINATION,  IN  PRESENCE  OF  MINERAL  ACID, 
OF  AN  AMINE  WHICH  COUPLES  READILY,  WITH  AN  AMINO- 
NAPHTHOL  SULPHONIC  ACID  WHICH  COUPLES  WITH  DIFFICULTY  : 

Direct  Deep  Black  EW  (Bayer). 

Formula  :  NH2  OH 

-No— 


(Benzidine.} 

/\ 


-N 


(Diamine.) 

In  the  case  of  Diamine  Green  B  we  have  become  acquainted  with 
a  mineral-acid  coupling  of  H-acid  with  ^-nitraniline,  and  have  seen 
that  these  components  combine  readily  to  give  a  monoazo  dye  in 
which  the  azo  group  is  attached  in  the  ortho  position  to  the  amino 
group.  Benzidine  couples  far  less  readily,  and  it  is  necessary  to 
neutralize  continuously  the  mineral  acid  which  is  set  free.  Contrary 
to  the  data  given  in  the  patent  literature,  it  is  not  possible  to  carry  out 
this  reaction  in  acetic  acid  solution,  since  H-acid  in  presence  of 
sodium  acetate  at  once  couples  in  the  ortho  position  to  the  hydroxyl. 
This  fact  has  given  rise  to  many  patent  actions,  which,  however, 
have  all  been  decided  in  favour  of  the  patentee  of  the  mineral-acid 
coupling  process. 

(a)  The  intermediate  compound  : 

NH2OH 

/y\ 

H03sl    X    JS03H 


126  DYES 

19*2  Gms.  of  100  %  benzidine  are  diazotized  as  described  on 
Benzidine,       P-   IIO>  and  the  temperature  reduced  to  10-12°.     To  this  tetrazo 
tetrazotized.     solution  is  added  during  the  course  of  an  hour  the  filtered  solution 
34-1  gms.        of  34' i  gms.  H-acid  dissolved  in  5*5  gms.  soda  and  300  c.cs.  of  water. 
The   H-acid  solution  should  react  distinctly  acid  to  the   litmus. 

55  gms.  "* 

Na2CO3.         Stirring  is  continued  at  12°  for  3  hours,  after  which  a  solution  of 

300  c.cs.          5- 5  gms.  soda  in  60  c.cs.  water  is  run  in  very  cautiously  during  2  hours, 

5-5  gms  care  t>em§  taken  that  the  mineral  acid  reaction  never  disappears  for  a 

Na2CO3  in      moment.     After  a  further  3  hours  at  12°  sufficient  dilute  sodium 

60  c.cs.  H2O.  carbonate  solution  is  added,  if  necessary,  to  give  a  faint  but  distinct 

reaction  with  Congo  paper,  the  mixture  then  being  allowed  to  stand 

all  night  in  a  cool  place.     The  reaction  for  benzidine  (with  H-acid 

solution),  and  also  that  for  H-acid  (with  diazotized  nitraniline),  by 

spotting   on   filter-paper,    will   have   disappeared   completely   after 

12  hours.     The  intermediate  compound  separates  out  as  a  powdery 

precipitate. 

(b)  The  intermediate  compound  : 

NH9OH 

S03H 


N2C1 

8- 8  gms  8*8  Gms.  of  pure  aniline  are  diazotized  as  described  on  p.  108,  and 

'  t^ie  diazonium  solution  is  added  to  the  first  intermediate  at  5°,  some 
ice  being  added  if  necessary.     The  mixture  is  well  stirred,  and  to  it 
26  gms.  is  added  very  rapidly  a  solution  of  26  gms.  soda  in  120  gms.  cold 

izo^ms  m      water.     It  will  be  seen  that  everything  goes  into  solution  almost 
H2O.  instantaneously,    after    which    the    new    intermediate    compound 

separates  out  completely.  An  excess  of  soda  must  not  be  used,  or 
else  a  portion  of  the  intermediate  compound  couples  up  with  the 
H-acid  next  to  the  hydroxyl  group.  The  course  of  the  reaction  may 
easily  be  followed  by  testing  the  rim  of  a  spot-test  on  filter-paper. 
It  sometimes  happens  that  the  diazo  benzene  reaction  does  not 
disappear  completely,  so  that  the  preparation  of  the  final  dye  is 
proceeded  with  after  a  quarter  of  an  hour. 


PLATE   XI. 


AZO   DYES  127 

To  the  second  intermediate  compound  are  added  u  gms.  of  n  gms. 
purest  m-phenylene  diamine  dissolved  in  a  little  water,  which  ^Upheny 
couples  up  rapidly  with  the  diazo  compound,  a  portion  of  the  colour-  diamine. 
ing  matter  formed  always  going  into  solution.  After  i  hour  at  14° 
the  product  is  heated  up  cautiously  to  50°,  and  10  gms.  sodium  * 
carbonate  are  added.  120  Gms.  salt  are  then  sprinkled  in,  after 
which  the  mixture  is  acidified  with  about  ao  c.cs.  concentrated  NaCl. 
hydrochloric  acid,  stirring  being  maintained  until  the  dye  is  com-  ??Q>CS'  conc' 
pletely  precipitated.  It  is  insoluble  in  a  10  %  solution  of  common 
salt  and  bicarbonate  at  50°,  so  long  as  it  has  not  previously  been 
boiled  up.  The  product  filters  very  readily  and,  after  pressing,  is 
dried  at  100°.  The  yield  is  about  100  gms.  of  strong  dye.  To  ensure 
that  the  dye  goes  properly  on  to  cotton  it  must  be  mixed  with  6  % 
of  its  weight  of  sodium  carbonate. 

By  the  use  of  m-toluylene  diamine  instead  of  phenylene  diamine, 
Deep  Black  V  is  obtained,  which  possesses  a  somewhat  more  reddish 
shade.  In  this  case  also  it  is  necessary  to  add  a  little  soda  after 
warming  up,  in  order  to  obtain  an  easily  filterable  product. 

Notes  on  Works  Practice. — The  cotton  black  just  described  is  the 
most  largely  used  direct  black  made  in  the  dye  industry.  It  is  used 
for  dyeing  all  manner  of  organic  materials  such  as  cotton,  wool- 
mixtures,  leather,  etc.  It  is  prepared  in  very  large  azo  plants,  only  the 
very  purest  intermediates  being  employed.  By  using  w-phenylene 
diamine  which  has  been  recrystallized  from  water,  the  highest 
yields  of  colour  are  obtained,  the  products  dyeing  pure  black  even 
when  the  dye-bath  is  approaching  exhaustion.  It  is  included  in  the 
so-called  "  Black  Convention  "  (Schwarz  Konvention)  concluded 
between  the  big  colour  factories  in  order  to  keep  the  price  up  to  a 
reasonable  level.  The  price  of  the  most  highly  concentrated  product, 
which  was  often  only  diluted  with  3  %  of  salt  and  5  %  of  soda,  was 
formerly  about  3  francs,  and  even  less,  per  kilo. 


Congo  Red. 

1 8*6  Gms.  of  commercial  benzidine  are  diazotized  as  described  i86gms. 
on  p.  no,  and  this  solution  mixed  with  50  gms.  100  %  naphthionate 

and  50  gms.  sodium  acetate  dissolved  in  200  c.cs.  water.     The  so  gms 

temperature  is  kept  for  an  hour  at  5°,  and  is  then  raised  slowly  to  Naphthion- 

20°,  and  kept  there  for  5  hours.     It  is  then  raised  to  30°,  and  stirred  J^'L^g 

for  24  hours  at  this  temperature,  which  is  increased  again  on  the  Sodium 

third  day  to  55°.     When  the  coupling  has  proceeded  for  two  and  a  ace 
half  days,  the  mixture  is  boiled  up  and  treated  with  40  gms.  of 


128  DYES 

calcined  magnesia,  which  precipitates  out  the  very  sparingly  soluble 
magnesium  salt  of  Congo  Red,  which  is  filtered  off  and  thoroughly 
washed.     In  this  manner  the  impurities  are  completely  removed. 
500  c.cs.          The  washed  magnesium  salt  is  pasted  up  with  500  c.cs.  of  boiling 
i  2   '  g  water,  and  is  then  decomposed  with  15  gms.  of  sodium  carbonate, 

Na,COi.  magnesia  being  precipitated  as  carbonate  and  the  dye  going  into 
solution  as  the  sodium  salt.  The  hot  solution  is  filtered,  the  mag- 
nesium carbonate  washed  with  water,  and  the  Congo  Red  pre- 
cipitated from  the  filtrate  by  means  of  15  (volume)  per  cent,  of 
common  salt.  The  colour  comes  out  as  a  bright  red  precipitate, 
and  after  drying  gives  a  yield  of  about  70  gms. 
Formula  : 

NH2 


N 


N 


Notes  on  Works  Technique  and  Practice. — In  spite  of  its  great 
sensitiveness  to  acids,  Congo  Red,  the  first  benzidine  colour  to  be 
made,  is  still  largely  used,  as  it  is  one  of  the  most  beautiful  of  the 
direct  cotton  colours.  It  is  only  prepared  by  two  or  three  factories 
at  the  present  time,  as  its  price  no  longer  allows  any  profit.  The 
commercial  product  containing  about  60  %  of  salt  costs  only  about 
70  centimes  per  kilo. 

On  the  large  scale,  the  coupling  is  often  carried  out  rather 
differently  from  the  laboratory  method.  The  coupling  may  be 
speeded  up  very  considerably  by  mixing  the  naphthionate  solution 
with  the  tetrazo-benzidine  solution  at  85°,  very  good  stirrirg  being 
of  course  essential.  Only  small  charges  can  be  worked  up  by  this 
method,  but,  on  the  other  hand,  it  is  possible  to  effect  8-10  couplings 
per  diem.  The  excess  naphthionate  is  frequently  recovered. 

Besides  Congo  Red,  Benzopurpurin  is  of  great  importance,  and 
is  prepared  from  o-tolidine  and  naphthionate.  In  this  case  it  is 
not  possible  to  carry  out  the  coupling  hot,  as  the  tetrazo  compound 


AZO   DYES  129 

of  tolidine  is  too  easily  decomposed.  This  colour  is  somewhat 
less  sensitive  to  acids  than  Congo  Red  and,  like  the  latter,  is  largely 
used  in  the  Orient.  It  would  appear  that  in  the  non-industrial 
countries  bordering  on  the  Mediterranean  Sea,  where  the  atmos- 
phere is  free  from  sulphurous  and  sulphuric  acids,  such  dyeings  are 
faster  than  they  are  with  us. 


MISCELLANEOUS  Azo  DYES, 
Tropseoline  or  Orange  IV 

(Azo  Yellow) 
from  Sulphanilic  acid  and  Diphenylamine. 

The  coupling  of  sulphanilic  acid  and  diphenylamine  affords  an 
interesting  example  of  a  mineral-acid  coupling.  In  this  case  it  is 
not  possible  to  work  in  either  neutral  or  alkaline  solution  as  the 
diazo-sulphanilic  acid  is  immediately  decomposed  by  sodium 
carbonate,  and  in  neutral  solution  it  refuses  to  react,  curiously 
enough.  Further,  diphenylamine  is  completely  insoluble  in  water, 
so  that  the  coupling  must  be  effected  in  aqueous-alcoholic  solution. 
It  is  indeed  possible  under  certain  conditions,  to  work  without  much 
alcohol,  but  in  this  case  so  much  unchanged  diphenylamine  remains 
that  it  becomes  difficult  to  nitrate  the  dye.  Besides  Orange  IV 
itself,  its  nitro  derivatives  are  also  valuable.  The  coupling  in 
alcoholic  solution  is  therefore  to  be  preferred  to  that  in  aqueous 
solution,  especially  as  the  yield  is  better,  so  that  in  this  way  the  small 
loss  of  alcohol  is  fully  made  up  for. 

As  already  noted  above,  diphenylamine  has  an  injurious  effect 
on  the  nitration,  and  other  impurities  which  accompany  Orange  IV 
possess  this  property  to  an  even  greater  extent.  If  it  is  intended  to 
convert  Tropaeoline  into  Azo  Yellow,  it  is  absolutely  necessary  that 
the  Tropaeoline  acid  shall  be  quite  pure,  as  slight  impurities  diminish 
the  yield  by  30-50  %.  If  a  pure  dye  is  available,  then  the  actual 
method  of  nitration  becomes  comparatively  unimportant.  This 
process  is  of  interest,  as  the  nitro  compound  is  obtained  via  the 
nitrosamine  and  nitramine,  the  Tropaeoline  being  nitrosated  with 
nitrous  acid  and  then  oxidized  with  very  dilute  nitric  acid.  The 
nitramine  is  formed  intermediately,  and  is  then  converted  at  once 
into  the  nitro  compound  under  the  influence  of  mineral  acid,  exactly 
as  Bamberger's  phenyl  nitramine  is  transformed  into  ortho-nitraniline. 


130 


DYES 


The  same  relationships  are  also  found  in  the  case  of  Methylene 
Green  (q.v.). 

Owing  to  its  pure  shade  and  satisfactory  fastness  to  light  and 
washing,  Tropaeoline  is  much  used  for  wool.  When  mixed  with 
certain  dyes  it  increases  their  strength  considerably.  This  is 
particularly  the  case  with  the  much-used  Acid  Black  46  (a  mixture 
of  about  45  %  Naphthol  Blue  Black  B  and  Naphthylamine  Black  D, 
together  with  5  %  each  of  Tropaeoline  and  Fast  Red  AV).  Attempts 
to  replace  Tropaeoline  in  this  case  by  other  yellow  colours  have  shown 
that  the  only  one  having  a  similar  action  is  Metanil  Yellow,  which  is 
formed  from  metanilic  acid  and  diphenylamine.  The  increase  in 
strength  amounts  to  about  30  %. 

For  silk,  the  acid-fast  Azo  Yellow  is  used,  which  goes  well  on  to 
silk  which  has  been  weighted  with  tin  phosphate.  For  the  pro- 
duction of  yellow  and  brown  shades  fast  to  water  Azo  Yellow  has 
become  indispensable. 


(a)  Tropceoline  or  Orange  IV. 


Reaction 


No  -% 


52  gms. 
ioo  % 
Sulphanilic 
acid. 
16  gms. 
Na2C03. 
300  c.cs. 
H20. 


35 
66°  Be. 
H2S04. 
22  gms. 
NaN02. 
250  c.cs. 

90% 

Alcohol. 


HC1 

+      NH—  -> 


-NH 


Orange  IV  or  Tropceoline. 


Diazo-sulphanilic 

acid.          \y 

Diphenylamine. 

52  Gms.  (3/10  mol.)  ioo  %  sulphanilic  acid  are  dissolved  in 
1 6  gms.  soda  and  300  c.cs.  of  water,  any  excess  of  aniline  being 
boiled  off.  The  solution  is  filtered  off  from  impurities  and  is  then 
acidified  with  35  gms.  concentrated  sulphuric  acid.  The  temperature 
is  reduced  to  12°  by  external  cooling,  after  which  the  liquid  is  diazo- 
tized  with  22  gms.  sodium  nitrite  dissolved  in  a  little  water.  After 
an  hour,  the  sparingly  soluble  diazo-sulphanilic  acid  is  filtered  off,1 
rinsed  out  on  to  the  nutsch  by  means  of  the  mother-liquor,  and  the 
crystals  pasted  up  with  250  c.cs.  of  90  %  alcohol.2  The  mixture 

1  In  a  moist  condition,  diazo-sulphanilic  acid  is  harmless,  but  when  quite  dry 
it  is  extremely  explosive. 

2  The  alcohol  must  not  be  denatured  with  pyridine  bases  ;  benzene,  however, 
does  no  harm. 


AZO    DYES  131 

is  cooled  to  12°  and  mixed  with  38  gms.  of  finely  divided  diphenyl-  38  gms. 
amine,  no  formation  of  colouring  matter  taking  place.     The  vessel  ^k|ny 
is  then  covered  with  a  lid  made  of  cardboard  or  lead,  and  12  gms.  I2  gms. 
concentrated  hydrochloric  acid  are  run  in  with  good  stirring.     The  3o% 
temperature  is  kept  at  12°  for  one  hour,  at  14°  for  2  hours,  and  for 
2  hours  at  18°,  the  temperature  of  the  water-bath  being  raised  finally 
to  35°.     The  dye  which  splashes  on  the  sides  of  the  pot  is  washed 
down  again  with  a  little  alcohol ;  no  evolution  of  gas  whatever  should 
be  noticeable  during  the  entire  reaction.     If  possible ,  stirring  is 
continued  for  a  further  6  hours,  and  next  day  the  product  is  diluted 
with  a  litre  of  water  at  50°.     The  insoluble  Tropaeoline  acid  is 
filtered  off  and  thoroughly  washed  with  water  until  the  washings 
are  a  pure  yellow.     The  product  is  then  taken  out  of  the  funnel  and 
the  curious  fact  will  be  noticed  that  the  apparently  solid  mass  becomes 
completely  liquid  as  soon  as  it  is  stirred  up  ;   in  the  works,  indeed, 
this  phenomenon  is  a  definite  test  for  the  purity  of  the  acid  ;    the 
more  fluid  the  product  is  which  is  obtained  from  the  solid  press-cake, 
the  purer  is  the  Tropaeoline.     The  glistening,  greyish-blue  product 
is  now  pasted  up  with  200  c.cs.  of  water,  boiled,  and  treated  with  200  c.cs. 
30    gms.    of    potassium    carbonate.     The    beautifully    crystalline    o2  ^s 
potassium  salt  of  the  dye  separates  out  completely  within  24  hours  K2CO3. 
and  is  then  filtered  off  and  dried  at  100°.     Yield  about  75  gms.  con- 
centrated product.    (The  sodium  salt  is  sparingly  soluble  and  un- 
attractive in  appearance,  for  which  reason  it  is  not  very  popular 
with  dyers.) 

(b)  Azo  Yellow  (Indian  Yellow,  Helianthine,  etc.), 
Reaction :  _^_ 

NaNO2  /— \  /~\       I       /—\    dil.  HNOo 

—2  NaO,SC       V-N2— <        )— N— / 


Sodium  salt  of  nitroso-tropceoline. 


Nitramine.  Azo  Yellow. 


The  fresh,  well- washed  Tropaeoline  acid  is  stirred  up  with  300  c.cs.  300  c.cs. 
of  water  and  treated  at  5°  with  16  gms.  of  100  %  sodium  nitrite.  **.2°' 
The  stirrer  must  be  run  very  slowly,  so  as  to  avoid  formation  of  froth,   \oo%' 
which  hinders  the  subsequent  nitration.     After  2  hours  the  pale  NaN°2- 


132 


DYES 


40  gms. 
60% 
HNO3 
(=40°  Be.). 


500  c.cs. 
H20. 

20  gms 

NaNO2. 
200  gms. 
NaCl. 


90  gms. 

60% 

HN03. 


100  gms. 
NaCl. 


500  c.cs. 
H2O 
30  gms. 
Na2C03. 


yellow  nitrosamine  has  precipitated  out,  and  40  gms.  of  60  %  nitric 
acid  are  added,  stirring  being  continued  for  a  further  2  hours.  The 
temperature  is  then  increased  cautiously  to  68°.  The  product 
begins  to  foam,  gradually  becomes  darker,  and  in  25  minutes  all 
has  gone  into  solution.  The  liquid  is  warmed  for  "a  further  10 
minutes  to  71°,  after  which  it  is  diluted  with  500  c.cs.  water, 
neutralized  with  25  gms.  sodium  carbonate,  and  the  Azo  Yellow 
precipitated  with  200  gms.  salt.  The  dye  separates  out  in  the  course 
of  a  day  as  an  orange-red  granular  precipitate,  which  is  filtered  off 
and  pressed  after  24  hours  ;  drying  is  effected  at  60°,  as  otherwise 
decomposition  occurs.  The  yield  is  about  100  gms. 

The  mother-liquor  is  always  strongly  coloured,  as  the  nitration 
never  goes  quite  smoothly,  since  a  certain  amount  of  nitro-diphenyl- 
amine  and  diazo-sulphanilic  acid  are  always  formed  from  the 
Tropaeoline  under  the  influence  of  the  nitric  acid.  The  formation 
of  the  diazo  compound  may  be  readily  recognized  if  a  drop  of  the 
nitration  mixture  be  taken  at  the  start  and  placed  on  filter-paper, 
on  touching  the  bright  yellow  rim  with  alkaline  H-acid  solution,  the 
red  azo  colour  from  sulphanilic  acid  and  H-acid  is  at  once  formed, 
indeed,  in  certain  factories  an  impure  Orange  II  (see  p.  113)  is 
prepared  from  the  acid  mother-liquor. 

The  Azo  Yellow  so  produced  is  not  sensitive  to  dilute  mineral 
acids,  but  does  not  meet  the  requirements  of  silk- dyers  for  certain 
purposes.  By  the  energetic  action  of  more  nitric  acid,  greener 
brands  are  obtained  which  are  quite  fast  to  acids. 

If  it  is  desired  to  manufacture  the  G  mark,  a  process  is  adopted 
which  differs  somewhat  from  the  ordinary.  90  Gms.  of  60  %  nitric 
acid  (instead  of  40  gms.)  are  taken,  and  the  nitration  is  begun  at  40°. 
The  temperature  is  raised  to  70°  during  2  hours  and  maintained  at 
this  point  for  a  further  2  hours,  the  resultant  dye  being  fast  to  acid. 
At  the  same  time  it  cannot  be  worked  up  without  further  treatment,  as 
it  comes  out  in  a  slimy  form  which  it  is  impossible  to  filter.  100  Gms. 
salt  are  therefore  added  to  the  nitration  liquid,  which  is  diluted  to 
i  litre  and  stirred  at  70°  until  the  precipitate  becomes  bright  orange 
and  powdery,  which  takes  from  1-2  hours.  The  liquid  is  now 
diluted  with  500  c.cs.  of  water,  and  then  worked  up  as  described  for 
Azo  Yellow.  The  yield  of  Azo  Yellow  G  is  about  85  gms. 

On  dissolving  in  hot  water,  the  nitrated  Tropaeolines  split  off 
nitrous  acid,  which  attacks  the  copper  apparatus  used  for  dyeing. 
For  this  reason  some  dyers  demand  an  Azo  Yellow  free  from  nitrous 
acid,  which  is  prepared  in  the  following  manner  :  the  freshly  filtered 
Azo  Yellow  is  heated  up  to  90°  with  four  times  its  weight  of  water, 


AZO   DYES  133 

by  which  means  the  greater  portion  of  the  nitrous  and  nitric  acids  are 
split  off.  After  about  3  hours  5  %  of  sodium  bisulphite  is  added, 
which  removes  the  last  traces  of  nitric  acid.  Red  gases  are  evolved 
from  the  mass  which  foams  up  somewhat  vigorously,  for  which 
reason  large  tubs  are  required.  By  this  treatment  about  15-20  % 
of  the  dye  is  always  lost  (cf.  also  Azo  Flavine  FF). 

Notes  on  Works  Technique  and  Practice. — The  diazotization  and 
coupling  of  the  sulphanilic  acid  is  effected  in  large  enamelled  vessels. 
The  stirrer  is  often  made  of  thick  glass  rods  which  are  fixed  into  a 
wooden  beam,  the  latter,  however,  not  coming  in  contact  with  the 
liquid.  The  diazosulphanilic  acid  is  separated  on  a  vacuum  filter 
(see  Plate  VI.).  Instead  of  an  enamelled  thermometer  tube,  one 
made  of  bamboo  may  be  used,  which  lasts  a  long  time.  When 
properly  prepared,  Tropaeoline  acid  must  be  quite  fluid  and  capable 
of  being  blown  out  easily  from  the  coupling  vessel.  After  the 
product  has  been  washed  out  in  the  filter-press  and  thoroughly 
blown  through,  the  moist  Tropaeoline  acid  from  38  kilos,  diphenyl- 
amine  weighs  almost  exactly  200  kilos.  A  variation  of  10  kilos,  more 
or  less  shows  that  impurities  are  present.  The  alcohol  is  recovered, 
and  after  neutralizing  with  soda  it  is  rectified  ;  about  15  %  is  lost 
on  each  operation. 

The  nitration  is  carried  out  in  tubs  made  of  pitch-pine,  and  holding 
about  2500  litres.  They  are  provided  with  a  good  ventilating  hood 
(see  Plate  VII.,  Fig.  6),  and  last  for  more  than  a  year.  The  point 
where  the  steam,  required  for  heating  up,  blows  into  the  tub  must  be 
protected  by  means  of  a  board  fixed  in  position  with  wooden  pegs. 


Aminoazobenzene  from  Aniline. 
Reaction  : 

NIL 


f  Aniline  salt 

r: — ~ 

f  aniline 


Diazoaminobenzene .  Aminoazobenzene , 


134  DYES 

250  gms.  250  Gms.  aniline  are  mixed  with  no  c.cs.  concentrated  hydro- 

chloric acid  in  a  glass  or  porcelain  beaker  with  good  stirring,  after 
cone.  HCI.  which  it  is  cooled  down  externally  to  32°,  and  45  gms.  100  %  sodium 
45  gms.  nitrite,  dissolved  in  a  little  water,  are  added  at  this  temperature 

NaNO2.          during  half  an  hour.     The  temperature  must  not  be  allowed  to 
exceed  34°.     After  2  hours  the  temperature  is  raised  to  40°,  and 
after  a  further  hour  it  is  kept  for  3  hours  at  46°.     The  mixture  is  now 
250  gms.         shaken  out  into  a  porcelain  basin  holding  250  c.cs.  of  water  and 
250  gms          25°  §ms-  ice>  concentrated  hydrochloric  acid  being  then  added  until 
Ice.  the  reaction  is  distinctly  acid  to  Congo.     The  excess  of  aniline  goes 

200  c.cs.  HCI  jnj-o  solution  whilst  the  sparingly  soluble  aminoazobenzene  hydro- 
chloride  remains  undissolved  ;  about  200  c.cs.  hydrochloric  acid  are 
required.  The  hydrochloride  is  filtered  off,  thoroughly  washed 
with  10  %  brine  containing  2  %  hydrochloric  acid,  and  finally 
with  2  %  hydrochloric  acid.  The  product  is  dried  at  50°,  taking 
care  to  avoid  any  over- heating,  as  otherwise  blue-black  dyes,  the 
so-called  Indulines,  are  formed  very  readily  by  internal  condensation. 
The  yield  of  pure  dry  aminoazobenzene  hydrochloride  amounts  to  about 
125  gms.  For  the  preparation  of  dyes,  the  free  base  is  not  isolated, 
the  hydrochloride  being  always  used. 

Fast  Yellow. — Fast  Yellow  is  the  disulphonic  acid  of  aminoazo- 
benzene. The  first  sulphonic  group  takes  up  the  para  position  to 
the  azo  group,  a  yellow  wool  dye  being  formed  which  only  satisfies 
very  modest  demands  as  to  fastness.  On  the  introduction  of  a  second 
sulphonic  group,  which  is  forced  to  take  up  the  ortho  position  to  the 
amino  group  (or  azo  group),  the  fastness  to  light  is  increased  to  a 
remarkable  extent. 

This  sulphonation  is  carried  out  very  simply :  One  part  amino- 
azobenzene hydrochloride  is  added  to  three  times  its  weight  of  25  % 
oleum  with  stirring  at  25°  until  a  test  portion  dissolves  easily  in 
sodium  carbonate.  The  temperature  is  then  raised  to  40°,  the 
stirring  being  continued,  and  is  heated  until  a  portion  dissolves 
completely  in  a  large  excess  of  water  ;  this  will  require  about 
5  hours.  The  finished  sulphonation  mixture  is  then  poured  on 
to  six  times  its  weight  of  ice,  after  which  the  mono-sodium  salt 
of  the  disulphonic  acid  is  salted  out  with  200  gms.  common  salt. 
The  flesh-coloured  precipitate  is  filtered  off,  thoroughly  washed 
with  15  %  brine,  and  the  filter-cakes  then  stirred  up  with  a 
little  water.  Sodium  carbonate  is  added  at  50°  until  the  colour 
becomes  a  pure  yellow,  a  greater  or  lesser  quantity  being  required 
according  to  the  thoroughness  of  the  washing.  Fast  Yellow 
cannot  be  salted  out,  but  is  evaporated  directly  to  dryness 


AZO   DYES  135 

below  90°.      The  yield  amounts   to  about  200   %   on   the  starling 
material. 

On  the  large  scale  aminoazobenzene  is  prepared  in  large  enamelled 
vessels  holding  300-400  litres.  The  acidification  is  carried  out  in 
ordinary  wooden  tubs,  and  the  mother-liquors  are  worked  up  for 
aniline  with  the  aid  of  line  and  steam,  the  loss  amounting  to  about 

15  %• 

In  spite  of  opinions  to  the  contrary,  Fast  Yellow  is  not  so  fast  to 
light  as  Tartrazine,  and  is  much  less  fast  than  those  pyrazolone 
colours  which  possess  a  sulphonic  group  ortho  to  the  azo  group. 
Aminoazobenzene  is  an  important  intermediate  for  many  disazo 
dyes  :  if  it  is  diazotized  and  allowed  to  act  upon  phenols,  naphthols, 
and  other  coupling  components,  secondary  disazo  dyes  are  produced, 
the  earliest  of  which  (aminoazobenzene  sulphonic  acid  ->  /3-naphthol) 
was  the  so-called  Biebrich  Scarlet.  For  this  reason  such  secondary 
disazo  colours  are  termed  dyes  of  the  Biebrich  Scarlet  type.  The 
diazotization  of  aminoazobenzene  takes  several  hours  ;  the  freshly 
prepared  aminoazobenzene  hydrochloride  is  suspended  in  5  parts 
of  water  and  a  further  150  gms.  hydrochloric  acid  is  added  for  each 
molecule  of  hydrochloride.  It  is  also  necessary  before  carrying  out 
the  actual  diazotization  to  estimate  approximately  how  much  sodium 
nitrite  will  be  required,  by  working  up  a  small  test  portion  at  great 
dilution.  The  diazotization  of  aminoazobenzene  is  effected  at 
10-14°,  and  often  takes  a  whole  day  on  the  large  scale.  The  finished 
diazotized  product  is  then  either  worked  up  at  once  or  cooled  down 
to  o°  by  means  of  ice. 

Owing  to  the  presence  of  the  amino  group,  aminoazobenzene 
may  be  condensed  with  dinitrochlorbenzene  exactly  as  is  the  case 
with  aniline  ;  the  product  is  Benzene-azo-dinitro-diphenylamine, 
which  is  a  beautifully  crystalline  and  almost  insoluble  substance. 
This  can  easily  be  converted  into  the  monosulphonic  acid  by  means 
of  sulphuric  acid  monohydrate,  a  nitro-azo  dye  being  produced 
which  has  exactly  the  same  empirical  formula  as  Weiler-ter-Meer's 
Azo  Yellow,  described  on  p.  131.  It  is,  however,  distinguished  from 
this  by  its  complete  homogeneity,  and  does  not  split  off  any  nitrous 
acid  on  boiling.  For  this  reason  some  silk  dyers  prefer  it  to  ordinary 
Azo  Yellow,  although  its  price  is  somewhat  higher. 


136 


DYES 


Reaction  : 


NH, 


Azo  Flavine  FF.  (B.A.S.F.) 
N02 


Cl 

O 

N02 


(basic  substance  to 
remove  acid) 


NO, 


NH 


NO, 


NO, 


NH 


100  gms. 
Aminoazo- 
benzene HC1, 
100  gms. 
Dinitrochlor- 
benzene. 
250  gms. 
Na  Acetate. 
600  gms. 

no  °/ 

y°  /o 
Alcohol. 


Phenyl-azo-dinitro  • 
diphenylamine . 


S03H 

Azo  Flavine  FF. 


(a)  Condensation  of  Aminoazobenzene  with  Dinitrochlorbenzene. — 
100  Gms.  of   100  %  still  moist  aminoazobenzene  hydrochloride, 
100  gms.   dinitrochlorbenzene,  and  250  gms.  crystallized  sodium 
acetate  are  heated  up  with  600  gms.  alcohol  (90  %)  under  a  reflux 
for  6  hours  with  stirring.     The  condensation  product  separates  out 
in  the  form  of  reddish  brown,  glistening  crystals  which  are  filtered 
off  hot  and  washed  with  a  little  alcohol.     The  crystals  are  dried 
at  1 00°,  the  yield  being  about  115  gms. 

(b)  Sulphonation. — One   part   of   the    condensation   product   is 
added    to    three    parts    monohydrate    and   stirred    for    i    hour    at 
30°,  after  which  the  temperature  is  raised  carefully  to  45°.     After 
1-2  hours  a  test  portion  should  give  a  clear  solution  in  dilute  sodium 
carbonate.     The  product  is  now  poured  into  six  times  its  weight  of 
water,  and  the  dye  is  salted  out.     It  is  filtered  off  acid,  washed  with 
15  %  salt  solution,  and  then  dissolved  in  a  little  hot  water  with  the 
requisite  quantity  of  sodium  carbonate.     The  solution  is  salted  out 
with  15  (volume)  per  cent,  of  salt,  a  gelatinous  precipitate  of  the 
sodium    salt  being  first  obtained,  which,  however,  soon  becomes 
beautifully  crystalline  and  easily  filterable.     The  yield  from  100  gms. 
condensation  product  is  about  125  gms.  strong  dye.     Azo  Flavine  FF 
has  the  shade  of  the  lower  nitrated  Tropaeolines,  and  the  great 
resistance  to  acids  of  the  highly  nitrated  Azo  Yellow. 


AZO   DYES 


Fast  Light  Yellow  G  (Bayer). 

Bayer's  Fast  Light  Yellow  G  is  the  simplest  member  of  the 
Pyrazolone  series  of  dyes.  These  are  obtained  by  two  methods, 
(i)  from  dioxy-tartaric  acid  (other  a-diketones  are  also  used)  and 
phenyl-hydrazines,  (2)  from  phenyl-methyl-pyrazolones  by  coupling 
with  diazo  components.  The  second  method  is  simpler,  and  has 
therefore  largely  displaced  the  older  process,  although  large  quantities 
of  Tartrazine  (from  dioxytartaric  acid  and  phenyl-hydrazine  sul- 
phonic acid)  are  used  at  the  present  day.  The  pyrazolone  is  prepared 
from  a  given  phenyl-hydrazine,  e.g.  from  the  phenyl-hydrazine 
sulphonic  acid  described  on  p.  64,  and  aceto-acetic  ester,  which  is 
then  coupled  with  aniline.  Reaction  : 

CH 
CHX/^C.OH 


N 


CH3.C 


N— 


S03H 


i-Sulphophenyl-^-methyl-^-pyrazolone.  Fast  Light  Yellow  G. 

The  hydrogen  of  the  phenyl-methyl-pyrazolone  sulphonic  acid 
which  is  replaced  during  the  coupling  by  the  azo  group  is  marked 
with  an  asterisk.  This  hydrogen  atom  is  in  the  ortho  position  to 
an  hydroxyl  group  (+)  which  renders  possible  the  formation  of  the 
coupled  product.  It  behaves  exactly  like  the  hydroxy  groups  in 
phenols  and  naphthols,  and  can  bring  about  lake  formation  from  azo 
dyes  derived  from  ortho-amino-phenols  and  ortho-amino-naphthols. 
Dyes  of  the  following  type  are  produced  : 


OH 


OH 


In  this  manner  Erio  Chrome  Red  B  (Geigy)  is  produced  from 
i:2:4-amino-naphthol  sulphonic  acid  (described  on  p.  50),  and 
phenyl-methyl-pyrazolone  (from  phenyl-hydrazine  and  aceto-acetic 
ester)  ;  it  is  a  very  fast  chrome  wool  colour  : 

\ 


P      M        f 
**       x>2       V 

CHs.C/^C.OH     OH 


N 


N.C6H5 


Erio  Chrome  Red  B  (Hagenbach). 


'38 


DYES 


19*7  gms. 

100  % 

Phenyl- 

hydrazine 

sulphonic 

acid. 

80  gms. 

40% 

Acetic  acid. 

13  gms. 
Aceto-acetic 
ester. 
26  gms. 
"  Pyrazo- 
lone." 
6  gms. 
Na2CO3. 

120  C.CS. 

H2O. 

30  gms. 
Sodium 
acetate. 


9'  3 

Aniline 

(diazotized). 


(a)  i-Sulphophenyl-^-methyl-^-pyrazolone. — 197  Gms.     100    % 
phenyl-hydrazine  sulphonic  acid  are  suspended  in  80  gms.  of  40  % 
acetic   acid,  and  to  it  are  added  13  gms.  aceto-acetic  ester.     The 
whole  is  then  boiled  up  under  a  reflux  for  an  hour,  and  is  then  cooled 
down  to  1 5°  with  continuous  stirring,  after  which  the  thick  magma 
of  crystals  is  filtered  off.     The  yield  of  dry  substance  is  27  gms.  oj 
9°  %  pyrazolone.     It -is  estimated  by  means  of  diazotized  aniline 
in  acetic  acid  solution  (see  Analytical  Section). 

(b)  Fast  Light  Yellow  G. — 26  Gms.  (i/io  mol.)  100  %  sulpho- 
phenyl-methyl-pyrazolone   are    dissolved   in    120    c.cs.    water    and 
6  gms.  sodium  carbonate,  and  to  this  are  added  30  gms.  sodium 
acetate.     After  cooling  down  to  o°  it  is  mixed  with  a  diazo-benzene 
solution  prepared  from  9*3  gms.  aniline,  and  the  whole  is  stirred 
until  a  small   test-portion   precipitated  with   salt   no   longer  gives 
a  red  coloration  with  alkaline  resorcinol  solution,  which  requires 
from    4-6    hours.      The    mixture   is   then    boiled    up   and   salted 
out    with    100    gms.    common   salt.       The  yield  is  about  40  gms. 
strong  dye. 

These  Pyrazolone  colours,  particularly  the  more  complicated  ones, 
are  much  faster  than  Fast  Yellow  (see  p.  134).  Dyes  derived  from 
the  ortho-sulphonic  acids  of  aromatic  amines  such  as  />-toluidine- 
o-sulphonic  acid  or  ^-chloraniline-o-sulphonic  acid,  include  yellow 
colours  which  are  among  the  fastest  to  light  with  which  we  are 
acquainted.  The  fastness  to  light  can  be  still  further  increased 
by  using  chlorinated  phenyl-pyrazolone  for  the  synthesis  of  azo 
dyes,  in  place  of  sulphophenyl  pyrazolones.  An  example  of  this  is 
the  Xylene  Yellow  of  Sandoz,  which  is  being  increasingly  used  owing 
to  its  unexampled  resistance  to  light,  despite  its  relatively  high  price. 
There  are,  of  course,  almost  innumerable  possible  modifications, 
of  which  Geigy's  Polar  Yellow  $G  may  be  instanced.  This  has  the 
following  composition  : 


CH 


SO,H 


>— N- 


;C— N«--< 


p-Chloraniline-o-  j 

sulphonic  acid 

radical. 


OH 

Aceto-acetic 
ester  radical. 


p-Amino- 
phenol 
radical. 


p-Toluene 
sulphonic 
radical 


PLATE   XII. 


a  a-s 

^is 
Hi 

O    K    O 

ll" 

5^  o 

o 

$l* 

41.5     X 


S'-P  o 
w    rt 


AZO  DYES  139 

Polar  Yellow  $G  (Richard)  ;    Swiss  Cavalry  Yellow. 

Para-chlor-ortho-sulphophenyl-hydrazine  is  condensed  with  aceto- 
acetic  ester,  and  the  resultant  pyrazolone  coupled  with  diazo-£- 
aminophenol  in  acetic  acid  solution.  The  azo  dye  so  produced, 
which  is  sensitive  to  alkali,  is  treated  with  ^-toluene  sulphonic 
chloride  at  70°  in  presence  of  sodium  carbonate  and  i  molecule 
caustic  soda  lye,  by  which  means  the  hydroxyl  group  is  esterified. 
As  a  result  of  this  ester  formation  the  dye  becomes  quite  fast  to 
alkalis,  and  at  the  same  time  fast  to  milling  on  wool. 

Notes  on  Works  Technique  and  Practice. — The  manufacture  of 
the  pyrazolone  dyes  is  simple,  the  aryl-hydrazines  being  usually 
condensed  in  enamelled  vessels  so  that  as  little  as  possible  of  the 
expensive  substance  shall  be  lost.  The  diazotization  and  coupling 
do  not  call  for  special  remark. 


Chrysophenine  GOO. 
Reaction  : 


NH 


CH 

I! 

CH 
/\SO,H 


/ 


NH2 

Brilliant  Yellow.  Chrysophenine  GOO. 

34  Gms.  (i/io  mol.)  of  100  %  diamino-stilbene-disulphonicacid  34  gms. 

is  dissolved  in  n  gms.  sodium  carbonate  and  200  c.cs.  water,  and  D^mino" 

r.  i-          1  •  i   •  •    •          1  i  r  /  1  stilbene  di- 

arter  cooling  the  acid  is  reprecipitated  by  means  01  50  c.cs.  (about  sulphonic 

60  gms.)  of  30  %  HCl.     The  temperature  is  reduced  to  5°  by  means  acid- 
of  ice,  and  the  substance  is  diazotized  during  two  hours  with  14  gms.  NagCO  . 
100  %  sodium  nitrite.     At  the  end  a  slight  but  detectable  excess  of  60  gms. 
nitrous  acid  should  be  present.     Sufficient  ice  is  now  added  to  g^0 
reduce  the  temperature  to  o°  and  then  20  gms.  phenol,  liquefied  14  gms. 
with  a  little  water,  are  added.     To  the  well-stirred  suspension  of  ^°N°^ 
phenol  and  tetrazo  compound  is  added  very  rapidly  a  solution  of  20  gms2' 

Phenol.' 


140 


DYES 


50  gms. 
NaaCO3. 


100  gms. 
NaCl. 
About  100 
gms.  HC1. 


Press-cakes 
200  gms. 
50  gms. 
Na2C03. 
30  gms. 

NaOH. 
250  gms. 
Alcohol. 
About  40 
gms.  Ethyl 
chloride. 
About  i  litre 
10% 
NaCl 
solution. 


50  gms.  sodium  carbonate  dissolved  in  200  gms.  water.1  The 
amount  of  ice  should  be  so  calculated  that  the  temperature  after  the 
addition  is  8°.  All  goes  into  solution,  and  after  a  certain  time  a 
portion  of  the  Brilliant  Yellow  precipitates  out.  After  standing  for 
2  hours,  the  liquid  is  heated  to  70°,  and  100  gms.  salt  are  added, 
together  with  enough  hydrochloric  acid  to  ensure  complete  pre- 
cipitation of  the  dye,  but  without  causing  a  change  of  colour  from 
yellow  to  blue.  After  cooling,  the  product  is  filtered  off  and  sucked 
as  dry  as  possible  at  the  pump.  It  weighs  about  180  gms. 

Ethylation. — The  moist  press-cakes  are  made  up  with  water  to 
200  gms.,  and  are  treated  with  50  gms.  dehydrated  sodium  carbonate 
and  30  gms.  of  35  %  caustic  soda  lye.  The  pasty  mixture  is  placed 
in  a  stirring-  or  rotating- autoclave,  and  250  gms.  90  %  alcohol  are 
added.  The  autoclave  is  charged  with  40  gms.  ethyl  chloride,  as 
described  on  p.  74,  and  the  mixture  is  then  heated  to  100°  for 
10  hours  with  continuous  stirring  (maximum  pressure  6  atms.). 
After  cooling  and  opening  the  autoclave  the  contents  are  diluted 
with  two  volumes  of  10  %  salt  solution,  and  the  beautifully  crystalline 
dye  is  filtered  off.  Provided  that  the  diamino-stilbene-disulphonic 
acid  was  free  from  diamino-dibenzyl-disulphonic  acid,  the  product 
is  about  20  %  stronger  than  the  strongest  commercial  colour.  The 
yield  is  about  70  gms.  dry  concentrated  colour. 

Notes  on  Works  Technique  and  Practice. — Chrysophenine  is  the 
most  important  direct  yellow  dye.  Owing  to  its  fastness  to  light 
upon  wool,  silk,  and  cotton,  and  to  its  low  cost  of  production,  it  is 
almost  without  a  competitor.  In  addition  to  the  alkylation  with 
aqueous  alcohol,  the  lime  method  is  also  of  some  importance,  as 
in  the  presence  of  lime  the  alkylation  may  be  effected  in  aqueous 
instead  of  in  alcoholic  solution.  In  both  cases  it  is  essential  that 
the  alkyl  derivative  formed  be  precipitated  at  once.  Which  of  the 
two  processes  is  to  be  preferred  depends  upon  the  current  price  of 
alcohol.  The  alcohol  method  is  better,  as  it  gives  directly  a  finished 
product  of  great  strength  which  dissolves  to  a  clear  solution,  and  the 
pressure  during  the  process  does  not  exceed  6  atms.,  whereas  by  the 
lime  method  pressures  of  25  atms.  and  over  are  encountered. 

Chrysophenine  gives  a  characteristic  reaction  with  mineral  acids, 
which  colours  it  a  beautiful  blue.  It  is  of  scientific  interest  to 
notice  that  although  there  are  no  auxochromes  present  in  the 

1  Contrary  to  the  view  often  held,  phenol  does  not  couple  at  all  easily  with 
diazo  components.  Diazo-ethers  are  frequently  formed,  which  lead  to  the  idea 
that  a  true  azo  compound  has  been  produced.  By  carrying  out  the  coupling  as 
described  for  Brilliant  Yellow,  i.e.  by  first  mixing  the  mineral  acid  diazonium  com- 
pound with  phenol  (or  cresol),  and  then  adding  sodium  carbonate,  but  not  caustic 
soda,  the  azo  dye  is  obtained  in  far  better  yield. 


AZO   DYES  141 

sense  of  Witt's  theory  of  colour,  it  is  nevertheless  an  extraordinarily 
powerful  dye. 

The  end  of  the  alkylation  of  the  Brilliant  Yellow  may  be  recog- 
nized in  the  following  manner  :  a  small  test-portion  is  dissolved  in 
water  and  treated  with  a  few  drops  of  acetic  acid.  A  drop  of  the 
faintly  acid  solution  is  placed  on  filter-paper,  and  the  yellow  stain  is 
touched  with  10  %  sodium  carbonate  solution.  As  soon  as  the 
alkylation  is  completed  no  change  of  colour  towards  reddish  yellow 
or  red  should  be  noticeable.  On  the  large  scale  samples  are  taken 
from  time  to  time  by  means  of  a  special  stop-cock,  and  the  ethyl 
chloride  is  not  added  all  at  once,  but  in  portions  of  10-15  kilos.  The 
heating  is  done  by  means  of  a  steam-jacket ;  the  vessel  used  is  a 
horizontal  rotating  autoclave  with  horizontal  stirring  gear,  the 
stuffing-boxes  of  which  are  kept  well  cooled,  as  otherwise  the  alcohol 
dissolves  out  the  lubricant  at  once.  The  consumption  of  ethyl 
chloride  is  approximately  180  %  of  theory. 


Benzo  Fast  Blue  FR  (Bayer) 
from  Aniline,  Cleve-acid  and  J-acid. 


The  preparation  of  azo  colours  of  high  molecular  weight  is  one 
of  the  most  difficult  in  the  domain  of  azo  chemistry.  It  is  not 
possible  to  lay  down  general  rules,  and  the  following  recipe  is  offered 
simply  as  an  indication  of  the  methods  adopted.  It  is  essential  to 
use  pure  intermediate  products,  and  the  intermediate  stages  can  only 
be  worked  up  further  after  a  preliminary  purification.  The  dilution 
is  often  an  essential  point,  and  the  sensitiveness  to  alkalis  increases 
with  the  molecular  weight,  whilst  the  energy  with  which  the  coupling 
takes  place  rapidly  diminishes  with  the  increased  size. 

Almost  all  azo  dyes  of  the  type  : 

A— N2— B— N2— C— N2— D 

(e.g.  Naphthogene  Blue  4!*. ;  the  combination  Naphthylamine- 
disulphonic  acid-2:4:8 — Cleve  acid-ny — Cresidine — ^-Xylidine) 
dye  cotton  more  or  less  well  without  the  aid  of  mordants. 


142 


DYES 


If  A  is  an  amine  of  the  benzene  series  then  the  dye  will  be 
especially  fast  to  light  if  the  para  position  is  replaced  by  an  acetyl - 
amino  group,  or  by  an  ox"alylamino  group  :  NH.CO.COOH.  Thus 
p-ammo  acetanilide  affords  products  which  are  very  fast  to  light. 
H-acid  is  also  distinguished  by  the  fact  that  azo  colours  obtained 
from  it  are  very  fast  to  light  and  particularly  pure  in  shade  (Benzo 
Fast  Blue  FF).  In  addition  many  naphthylamine  disulphonic  acids 
are  of  importance  in  this  connection. 

As  regards  B  and  C  there  are  a  large  number  of  possibilities. 
Cleve  acids  1:6  and  1:7  are  used,  and  also  w-toluidine,  which 
differs  from  aniline  in  coupling  readily  with  azo  components,  ra- 
Amino-p-cresol  methyl  ether,  the  so-called  "  Cresidine,"  is  much 
used,  as  dyes  containing  this  component  possess  great  purity  and 
strength. 

As  to  D  two  compounds  are  of  special  importance,  namely 
aminonaphthol  sulphonic  acid  2:5:7  (J-acid)  and/>-xylidine.  Colours 
derived  from  ^-xylidine  may  be  diazotized  further  on  the  fibre,  and 
unite  with  naphthols  and  amines  to  yield  products  which  are  fast  to 
light  and  washing. 

As  may  be  seen  from  these  indications  the  possibilities  are  almost 
unlimited.  More  than  a  hundred  dyes  of  this  type  are  met  with  in 
commerce,  and  every  colour  factory  places  both  patented  and  free 
products  on  the  market. 


9*4  gms- 

diazotized 
Aniline  and 
Na  formate. 

22*3  gms. 

100  % 

Cleve  acid 

1:7. 

25  gms.  Na 

formate. 


20  gms. 

30% 

NaOH. 


(a)  Aniline-Cleve  acid-i:j. 

9*4  Gms.  pure  aniline  are  diazotized  as  described  on  p.  108,  and 
the  diazonium  solution  is  neutralized  by  means  of  sodium  formate, 
which  is  cheaper  than  the  acetate,  until  it  is  just  mineral  acid.  The 
neutralized  solution  is  added  to  22*3  gms.  Cleve  acid  1:7  dissolved 
in  300  c.cs.  water,  using  the  pure  sodium  salt  of  the  latter.  As  soon 
as  the  solutions  have  been  mixed,  a  further  25  gms.  sodium  formate 
in  concentrated  solution  are  added,  which  has  previously  been  made 
faintly  acid  to  litmus  by  means  of  formic  or  acetic  acids.  The 
aniline  combines  with  the  Cleve  acid  at  8°  within  5  hours,  but  it  is 
advisable  to  allow  the  coupling  to  stand  all  night,  as  this  is  the  only 
way  of  ensuring  that  a  uniform  dye  will  be  produced.^  Next  day 
20  gms.  caustic  soda  lye  (30  %)  is  added,  and  the  mixture  allowed  to 
stand  for  at  least  4  hours  at  20°.  (It  is  a  great  mistake  to  try  to 
work  up  such  couplings  too  quickly.)  A  valueless  azo  colour  is 
produced  which  must  now  be  diazotized  further  in  a  special 
manner. 


AZO   DYES  143 

(b)  Aniline-Cleve  acid-i:j — Cleve  acid-i:j. 

The  suspension  of  the  orange-yellow  monoazo  dye  is  treated  with 
60  gms.  common  salt  and  7*5  gms.  sodium  nitrite.     Sufficient  ice  60  gms. 
is  then  added  to  reduce  the  temperature  to  o°,  after  which  50  c.cs.  NaC1- 
concentrated  hydrochloric  acid  are   quickly  added  ;    the  reaction  NaNoJ 
should  be  distinctly  mineral-acid.     In  the  present  case  the  diazo-  (i°°  %)• 
tization  can  be  carried  out  only  in  presence  of  sodium  chloride,  and  Ice>to  °  • 

.     .  ,  ..  1  r      1  i-5°  gms« 

it  is  necessary  to  precipitate  out  the  sodium  salt  or  the  colouring  30  % 
matter  in  the  presence  of  NaCl  and  of  nitrite,  as  otherwise  the  diazo-  HC1- 
tization  is  almost  impossible.     A  similar  case  was  discussed  when 
dealing  with  the  diazotization  of  a-naphthylamine  (see  p.  109). 

The  temperature  may  be  allowed  to  rise  to  12°,  and  the  diazo- 
tization is  to  be  regarded  as  complete  when  nitrous  acid  can  be 
distinctly  noticed  after  2  hours.1  If  necessary,  a  little  sodium  nitrite 
may  be  added.  The  mixture  is  allowed  to  stand  all  night  at  10-12°, 
and  the  brown  diazo  compound  is  filtered  off  quickly  on  a  large 
nutsch.  Although  it  is  quite  stable,  it  must  be  protected  from  heat 
and  light.  The  mother-liquor  is  deeply  coloured  and  is  thrown  away. 

The  diazo  compound  is  now  stirred  up  with  400  gms.  ice-water  400  gms. 

to  a  thin  paste,  which  is  then  mixed  with  22"\  gms.  Cleve  acid  and  Ice~water- 

22'"?  gms. 

20  gms.  sodium  formate,  exactly  as  described  for  the  first  coupling.   100  % 

The  mixture  is  stirred  for  6  hours  at  5-7°,  and  is  then  allowed  to  cleve  acid 

1:7. 
stand  over-night,  after  which  it  is  heated  up  to  50°  and  allowed  to  20  gms  N 

stand  a  further  hour  at  this  temperature.     25  Gms.  of  30  %  caustic  formate, 
soda  solution  are  then  allowed  to  drop  in  during  one  hour,  the  dye  ^  If18' 
going  into  solution  with  a  blue- violet  colour.     Unfortunately  it  is  NaOH. 
not  possible  to  salt  out  the  dye  from  the  alkaline  solution,  which 
must  be  acidified.     At  the  same  time,  however,  various  impurities  100  gms. 
are  also  precipitated  which  are  carried  along  and  accompany  the  NaC1- 
finished  product.     After  the  addition  of  100  gms.  of  salt,  the  product  i°5  %^ 
is  acidified  with  about  50  c.cs.  of  15  %  hydrochloric  acid,  after  which  HC1- 
the  dye  is  filtered  off,  pasted  up  with  200  c.cs.  water  and  25  gms.  g>°oc-cs- 
caustic  soda,  and  completely  dissolved  up  at  90°.     7  Gms.  of  100  %  25  gms. 
sodium  nitrite  are  added  to  the  liquid,  and  the  clear  solution  is  then  NaOH- 
allowed  to  run  into  a  mixture  of  60  gms.  of  30  %  hydrochloric  acid,  10?*% 
400  gms.  ice,  and  300  c.cs.  water,  at  60°  during  half  an  hour.     Ice  NaNO2. 

60  gms. 

1  Such  diazo  compounds  are  deeply  coloured,  and  it  is  usually  not  possible  to    3°  % 
test  them  directly  for  nitrous  acid  by  means  of  nitrite  paper.     A  drop,  therefore,   **CI. 
of  the  solution  or  suspension  which  is  to  be  examined  is  placed  on  a  little  heap  of 
salt  lying  on  thin  filter-paper.     The  coloured  substance  is  precipitated  out  by  the 
salt,  and  by  pressing  the  reagent  paper  on  to  the  reverse  side  of  the  filter-paper  it 
can  readily  be  seen  if  mineral  acid  and  nitrous  acid  are  present  in  excess. 


144  DYES 

400  gms.  is  added  fast  enough  to  keep  the  temperature  constant  at  about  8°. 
300' c  cs.  The  total  vomme  at  tne  end  should  be  about  i  J  litres,  and,  if  a  pure 
H2O.  Cleve  acid- 1:7  has  been  used,  a  completely  clear  solution  of  the 

diazo  compound  will  result ;   this  again  cannot  be  precipitated,  as  it 

decomposes  readily. 

(c)  Aniline — Cleve  acid — Cleve  acid — J-acid. 

The  clear,  deeply  coloured  solution  of  the  diazo  compound  which 
has  the  formula  : 


>— N,— /      i\—  N9— 


XJL/ 

S03H 

20  gms.  is  allowed  to  drop  during  one  hour  into  a  solution  of  20  gms.  of 

fio<J~%).          IO°  %  J-acid  (aminonaphthol  sulphonic  acid  2:5:7),  60  gms.  soda, 

60  gms.  and  300  c.cs.  water.     The  temperature  must  not  exceed  o°,  and  must 

2      3>         be  regulated  by  means  of  ice.     Stirring  is  continued  for  an  hour, 

H2O.  and  next  day  the  mixture  is  boiled  up  in  a  porcelain  basin.    150  Gms. 

150  gms.         salt  are  then  added,  and  the  precipitate  filtered  off  at  80°.     The 

mother-liquor  is   highly   coloured   and   always   contains   a   certain 

amount  of  J-acid.     It  is  not  feasible  to  diminish  the  excess  of  J-acid, 

as  by  so  doing  the  yield  of  colour  is  diminished  in  proportion. 

The  precipitate  filters  slowly,  but  is  obtained  finally  almost  free 

from  salt,  as  it  is  in  a  good  crystalline  condition.     It  is  again  treated 

with  a  little  5  %  brine,  and  is  then  dried  at  100°,  the  resultant 

product  forming  a  fine    bronzed  powder  weighing  about  40  gms. 

Benzo  Fast  Blue  FR  dyes  cotton  in  blue  shades  which  are  fast  to 

light  and  are  superior  to  those  obtained  from  Indigo.     The  fastness 

to  chlorine,  however,  is  very  slight,  and  the  fastness  to  washing  only 

moderate.     Whether  the  preparation  has  been  carried  out  properly 

may  be  determined  not  only  from  the  yield,  but  also  from  the  exhaust. 

A  correctly  made  dye  will  give  exhausts  of  the  same  shade  as  the 

original  dyeing,  though  of  course  correspondingly  weaker. 

Notes  on  Works  Technique  and  Practice. — Dyes  of  this  class  are 
manufactured  in  ordinary  azo-colour  sheds  as  indicated  diagram- 
matically  on  Plate  VII.  Owing  to  the  instability  of  the  diazo- 
compounds  it  is  necessary  to  use  very  large  filter-presses  so  that  the 
whole  charge  may  be  put  through  in  one  operation.  It  is  then 
possible  to  work  up  the  diazo  compound  immediately  after  emptying* 


TRIPHENYLMETHANE  DYES 

the  filter-press.  It  is  also  advisable  to  manufacture  this  colour 
during  the  colder  season  of  the  year,  and  to  allow  only  very  trust- 
worthy men  to  deal  with  the  operation.  Again,  it  is  a  very  good  plan, 
whenever  possible,  to  carry  out  in  the  laboratory  the  next  operation, 
with  a  small  portion  of  the  intermediate  product  (e.g.  i/ioooth  part), 
before  the  actual  manufacturing  stage  is  begun  ;  by  this  means  many 
disappointments  will  be  avoided.  The  various  intermediate  products 
should  also  be  kept  as  samples  in  a  pure  form  so  that  by  careful 
comparison  one  may  judge  whether  the  process  is  pursuing  a  normal 
course. 


7.  TR1PHBNYLMETHANE  DYES 

Malachite  Green. 
Formula.1 

N(CH3)2' 

o 

\/ 

— C H,O      Cl 


N(CH3)2  ^ 


(a)  Leuco-Malachite  Green. 

37*8  Gms.  (3/10  mol.)  dimethylaniline,  24  gms.  (2/10  mol.) 
30  %  hydrochloric  acid,  and  io'6  gms.  (i/io  mol.)  benzaldehyde  are 
placed  in  a  300  c.c.  bolthead  and  the  mixture  heated  up  for  12  hours 
with  a  reflux-condenser.  To  prevent  the  oxidation  of  too  much 
aldehyde,  the  end  of  the  condenser  is  closed  with  a  plug  of  cotton- 
wool. It  is  necessary  to  stir  vigorously  during  the  whole  reaction. 
At  the  end  of  this  time  the  benzaldehyde  will  have  disappeared 
almost  completely.  12  Gms.  anhydrous  sodium  carbonate  are  added, 
and  the  excess  of  dimethylaniline  is  driven  off  with  steam,  and  may 
be  readily  recovered.  The  residual  leuco  base  of  Malachite  Green 
is  separated  from  the  water  after  cooling,  powdered,  and  again 
washed .  The  yield  of  dry  product  is  about  24  gms. 

1  The  formula  of  Malachite  Green  is  given  here  in  accordance  with  the  scheme 
put  forward  in  Helvetica  Chimica  Acta,  1918,  part  3. 

IO 


37'8  gms. 
Dimethyl- 
aniline. 
24  gms. 
30% 
HC1. 
10*6  gms. 
Benzalde- 
hyde. 

12  gms. 
Na2C03. 


146 


DYES 


16*5  gms. 
Leuco  base. 
300  c.cs. 
H20. 
20  gms. 


+  Ice. 
II'Q  gms. 
PbO2. 
25  gms. 
Na2SO4,  or 
10  gms. 
66°  Be. 
H2S04. 
15  gms. 
Na2CO3. 


120  gms. 
"  Base." 
72  gms. 
cry  st. 

Oxalic  acid. 
300  c.cs. 
H20. 


Reaction  : 


(b)  Oxidation  of  Leuco  Base  to  Colour. 


N(CH,). 


PbO.; 


N(CH3)2 


— C.OH 


N(CH3)2 


N(CH3)2 


Oxidation  is  effected  in  dilute  aqueous  solution  with  the  exactly 
calculated  quantity  of  lead  peroxide  (see  analytical  section).  On 
the  laboratory  scale  it  is  possible  to  obtain  a  lead  peroxide  paste 
of  exact  composition,  without  resorting  to  analysis,  by  dissolving  a 
weighed  portion  of  lead  nitrate  in  water  and  treating  with  calcium 
hypochlorite  solution  until  all  the  lead  is  precipitated.1  The  pre- 
cipitated peroxide  is  then  washed  with  plenty  of  water  and  used  as  a 
moist  paste. 

i6'5  Gms.  (1/20  mol.)  pure  leuco  base  are  dissolved  in  300  c.cs. 
water  and  20  gms.  strong  hydrochloric  acid,  and  the  solution  made 
up  to  400  c.cs.  at  o°  with  ice.  The  liquid  is  well  agitated  and  to  it 
is  added  quickly  a  peroxide  paste  from  exactly  i  /2Oth  molecule  lead 
nitrate  (=i5'5  gms.).  After  2  hours  a  solution  of  25  gms.  Glauber 
salt  is  added,  the  lead  being  precipitated  as  the  insoluble  sulphate, 
which  is  removed  by  filtration.  The  colour  base  is  now  precipitated 
by  means  of  15  gms.  anhydrous  sodium  carbonate,  and  is  filtered  off  ; 
usually  it  comes  out  in  a  resinous  form.  The  yield  of  dry  product  is 
about  1 6  gms.,  or  almost  100  %  of  theory. 

(c)  Crystallization  of  Malachite  Green. 

It  is  not  easy  to  effect  the  crystallization  in  the  laboratory  as  large 
quantities  are  required  for  the  production  of  fine  crystals.  120  Gms. 
base  (or,  better,  several  times  this  amount)  are  dissolved  in  72  gms. 
crystallized  oxalic  acid  and  300  gms.  distilled  water,  and  the 

1  Calcium  hypochlorite  is  very  soluble,  like  calcium  chloride  ;  the  insoluble 
residue,  after  treating  with  water,  consists  of  lime  and  chalk.  All  heating  must 
be  avoided. 


TRIPHENYLMETHANE   DYES  147 

impurities  filtered  from  the  boiling  liquid.  A  very  concentrated 
solution  of  7  gms.  ammonium  oxalate  is  then  added  to  the  hot  7 
liquid,  and  the  mixture  allowed  to  stand  away  from  draughts.  The 
best  plan  is  to  place  the  vessel  containing  the  solution  inside  another 
larger  vessel  filled  with  hot  water,  so  as  to  allow  the  former  to  cool 
down  slowly.  The  temperature  is  now  allowed  to  cool  during  the 
course  of  a  day  to  70°,  when  the  fine  crystals  are  filtered  off.  A 
further  quantity  of  less  pure  dye  separates  out  from  the  mother- 
liquor  on  cooling,  and  forms  the  Malachite  Green  II.  of  commerce. 
The  yield  from  one  part  of  leuco  base  may  be  up  to  i  '45  parts  oxalate  or 
145  %  by  weight  of  the  initial  material. 

Notes  on  Works  Technique  and  Practice. — Malachite  Green  is 
still  a  very  important  product,  and  serves  for  dyeing  tin- weighted 
silk,  wool,  and  paper.  Mixed  with  other  dyes,  it  yields  pure  mixed 
shades  which  are  very  cheap,  but  possesses  only  moderate  fastness. 
It  is  also  used  for  printing  on  silk  and  cotton,  but  for  these  purposes 
its  fastness  is  not  adequate  to  modern  demands,  so  that  its  use  is 
diminishing. 

The  condensation  is  effected  nowadays  only  with  mineral  acid, 
the  old  zinc  chloride  method  having  long  been  given  up  ;  Doebner's 
method,  also,  starting  from  berizotrichloride,  is  no  longer  utilized. 
The  condensation  is  effected  by  means  of  hydrochloric  or  sulphuric 
acid.  Hydrochloric  acid  effects  the  condensation  more  quickly, 
but  requires  the  use  of  enamelled  apparatus,  whilst  the  sulphuric 
acid  condensation  may  be  carried  out  in  homogeneously  lead-lined 
vessels.  It  is  important  not  to  use  too  much  acid  or  else  the  con- 
densation goes  to  a  certain  extent  in  another  direction,  a  benzydrol  of 
the  following  formula  being  produced  as  a  by-product  : 

OH 

"~^  N(CH3)2 


which  is,  of  course,  incapable  of  giving  the  required  dye  by  oxidation. 
Various  fractions  are  obtained  when  working  on  the  large  scale, 
as   different   customers   demand   products   of  varying  appearance. 
The  oxalate  of  Malachite  Green  has  the  formula 

2xC23H24N2+3xC2H204. 

The  crystallization  may  occupy  several  days  when  working  with 
quantities  of  from  one  to  six  cubic  metres,  and  crystals  are  frequently 


148 


DYES 


obtained  of  considerable  beauty.  The  addition  of  ammonium 
oxalate  to  start  the  crystallization  is  reminiscent  of  similar  relation- 
ships in  alkaloid  chemistry  and  is  a  purely  empirical  discovery. 
For  further  details  see  under  Xylene  Blue. 


Xylene  Blue  VS  (Sandoz). 

Xylene  Blue  belongs  to  the  so-called  Patent  Blue  class,  which 
includes  sulphonated  triphenylmethane  dyes  which  are  fast  to 
alkalis.  These  products  all  have  the  common  factor  that  the  sul- 
phonic  group  is  in  the  ortho  position  to  the  methane  carbon  atom. 
The  general  formula  is  therefore  : 


Na 


Sandmeyer  was  the  first  to  recognize  the  connection  between 
constitution  and  stability  to  alkalis,  and  his  Erioglaucine,  the  formula 
of  which  is  given  below,  was  the  first  colour  to  .be  prepared  in  the 
light  of  this  important  knowledge  : 


Erioglaucine  ( Sandmeyer) . 

(S03.C6H4.CH2— N— C6H4)2-C— 

I  I 

CTT  Q.C\    ' 

2hL5  oU3 


Na2 


from    Ethylbenzylaniline    sulphonic    acid   and   Benzaldehyde    ortho- 

sulphonic  acid. 

Probably  an  internal  anhydride  is  formed  between  the  carbinol 
hydroxyl  and  the  sulphonic  group,  and  to  this  is  due  the  great 
stability  towards  sodium  carbonate  and  caustic  soda.  This 
hypothesis  is  not  a  mere  wild  guess,  but  is  strongly  supported  by  the 
fact  that  dyes  of  the  formula — 


TRIPHENYLMETHANE   DYES 


149 


are  quite  insoluble  in  alkalis. 
Reaction  : 


CH. 


(a)     CH3 
/i\S03H 


Toluene. 
I. 


SO3H 

Toluene  disulphonic 
acid  1:2:4. 

II. 


N(C2H6)2 


HO,S<i       h— CH 


N(C2H5)2 

Leuco-Xylene  Blue  VS. 

IV. 


(b)    CHO 

/i\S03H 

21 


SO3H 

Benzaldehyde  disulphonic 
acid  1:2:4. 

in. 


N(C2H5)2 


.OH 


N(C2H5)2J 

Xylene  Blue  VS  (Steiner). 

V. 


Na< 


(a)  Toluene  disulphonic  acid.     II. 

46  Gms.  pure  toluene  (J  mol.)  are  mixed  with  80  gms.  sulphuric  46  gms. 
acid  (monohydrate)  by  dropping  the  acid  into  the  boiling  toluene     °  ^e' 

during  a  quarter  of  an  hour  and  then  heating  to  125°  for  an  hour.  100  % 
The  toluene  will  have  completely  disappeared  by  this  time,  and  the 


DYES 


220  gms. 

66% 

Oleum. 


400  gms. 

66% 

H2SO,. 


mixture  is  then  cooled  down  to  30°,  after  which  220  gms.  of  66  % 
oleum  is  run  in  during  half  an  hour.  The  product  is  heated  up  to 
125°  for  4  hours,  all  the  toluene  being  thereby  converted  into  the 
disulphonic  acid.  The  mixture  is  then  diluted  with  400  gms.  of 
sulphuric  acid  (66°  Be.)  and  the  whole  transferred  to  a  porcelain 
pot  provided  with  a  good  iron  stirrer. 


100  gms. 
MnO2  as 
Mn3O4. 


Approx.  25° 
gms.  CaO. 


About 
50  gms. 
Na2C03. 


(b)  Benzaldehyde  disulphonic  acid.     III. 

The  product  is  treated  by  degrees  with  125  gms.  80  %  manganese 
paste  in  small  portions,  with  good  stirring.1 

The  addition  should  occupy  half  an  hour,  the  temperature  of  the 
mixture  being  about  25°.  When  the  addition  is  completed,  the 
product  is  stirred  for  a  further  3  hours  at  30°,  and  the  temperature 
is  then  raised  to  120°.  At  this  temperature  the  mixture  usually 
becomes  so  thick  that  stirring  is  impossible.  The  dark  colour  of  the 
manganese  dioxide  gradually  changes  to  a  pale  grey.  It  is  rarely 
possible  in  the  laboratory  to  effect  the  oxidation  so  completely  that 
all  the  dioxide  disappears,  and  it  is  necessary  to  stop  the  reaction 
before  this  point  is  reached.  After  standing  for  12  hours  the  mass  is 
diluted  with  2  litres  water  and  slaked  lime  added  until  the  mineral 
acid  reaction  has  completely  disappeared. 

Litmus,  however,  should  not  be  turned  a  pronounced  blue,  as 
any  excess  of  alkali  destroys  the  aldehyde  sulphonic  acid.  The 
pasty  mass  of  calcium  sulphate  is  now  treated  with  strong  sodium 
carbonate  solution  until  a  filtered  test-portion  no  longer  gives  a 
precipitate  on  adding  sodium  carbonate.  The  solution  is  filtered 
from  the  calcium  sulphate  and  manganese,  the  precipitate  well 
washed,  and,  if  possible,  the  gypsum  again  pasted  up  with  water  and 
filtered.  The  faintly  alkaline  filtrate  is  evaporated  down  in  vacuo 
to  250  c.cs.,  and  is  then  filtered,  if  necessary,  from  any  traces  of 
calcium  sulphate  or  manganese  oxide.  The  yield  may  be  estimated 
by  treating  an  aliquot  part  of  the  solution  in  presence  of  sodium 
acetate  with  a  solution  of  phenyl  hydrazine  acetate  of  known  strength 
until  a  portion,  after  salting  out,  no  longer  reacts  on  a  further  addition 
of  "  hydrazine."  With  this  reagent  an  intense  yellow  coloration 
is  at  once  produced  ;  the  method  of  estimation  is  not  very  accurate, 
however. 

1  The  manganese  paste  is  calculated  as  MnO2,/.e.  exactly  100  gms.  of  manganese 
dioxide  is  used  in  the  form  of  the  so-called  "  Manganese  Mud,"  which  is  a  waste 
product  from  the  manufacture  of  saccharine  and  possesses  the  approximate 
formula  Mn3O4.  For  estimation,  see  Analytical  portion. 


PLATE   XIII. 


M.P 


" 


1 


TRIPHENYLMETHANE   DYES  151 

(c)  Condensation  to  leuco  compound.     IV. 

The  whole  solution  is  boiled  up  with  45  gms.  sulphuric  acid  and 
100  gms.  pure  diethyl  aniline  for  two  days  under  a  reflux,  after  which 

the  mixture  is  made  alkaline  by  means  of  100  gms.  30  %  caustic  100  gms. 

soda  lye,  and  the  excess  of  diethylaniline  is  driven  off  with  steam.  ^J^J1" 

If  necessary  the  alkaline  solution  is  filtered  and  is  then  made  just  I00  gms. 

acid    with    50    gms.    concentrated    sulphuric    acid.     The    internal  39  % 

anhydride  of  the  leuco  compound  is  precipitated  in  the  course  of  About  50 

24  hours  as  fine  white  needles,  which  are  filtered  off  and  thoroughly  gms.  cone, 
washed  out  with  water.     After  drying  thoroughly  at  80°  they  weigh      *     4> 
70  gms. 

(d)  Oxidation  to  the  Dye.     V. 

The    oxidation   closely   resembles    that   for   Malachite    Green.  5°  gms. 
50  Gms.  of  the  leuco  compound  are  dissolved  in  a  boiling  solution  of  compound. 
8  gms.  anhydrous  sodium  carbonate,  as  the  sparingly  soluble  leuco  8  gms. 
compound  is  practically  insoluble  in  cold  soda  solution.     The  liquid      a*      3' 
should  be  perfectly  neutral  to  litmus,  and  is  made  up  to  1800  c.cs.  at  H2SO4. 
o°.     A  mixture  of  15  c.cs.  concentrated  sulphuric  acid  and  exactly  22  gms. 
22  gms.  100  %  lead  peroxide  paste  is  added  in  one  operation  to  the.  I0o  %. 
mixture  (cf.  Malachite  Green). 

After  standing  an  hour  at  0-5°  the  product  is  heated  to  80°  and 
the  lead  sulphate  filtered  off.  The  solution  is  evaporated  down  to 
150  c.cs.,  preferably  in  vacuo,  and  50  gms.  salt  are  added.  The 
finished  dye,  which  comes  out  in  a  beautifully  crystalline  form  during 
the  course  of  a  day,  is  filtered  off  and  washed  with  a  little  saturated 
brine.  It  is  then  dried  in  a  small  porcelain  basin,  after  adding  a 
drop  of  ammonia  to  neutralize  any  remaining  trace  of  mineral  acid. 

Yield  of  concentrated  dye  =  32  gms. 

Notes  on  Works  Technique  and  Practice.— -The  benzaldehyde 
disulphonic  acid  is  so  easily  soluble  that  it  is  not  possible  to  isolate 
it.  The  oxidation  is  effected  in  large  kneading  troughs  with  inter- 
lacing arms  such  as  were  first  built  by  Werner  and  Pfleiderer.  The 
apparatus  may  be  heated  by  means  of  a  steam  jacket,  and  owing  to  its 
powerful  construction  the  mixing  may  be  continued  right  up  to  the 
end.  By  this  means  it  is  possible  to  work  with  rather  less  sulphuric 
acid  than  indicated  above.  Liming  and  evaporation  are  carried  out 
by  known  methods,  but  one  difficulty  shows  itself.  The  heating 
tubes  become  very  quickly  encrusted  with  calcium  sulphate,  and 
owing  to  the  sensitiveness  of  the  aldehyde  disulphonic  acid  it  is  not 
possible  to  use  any  excess  of  soda  in  order  to  precipitate  the  lime 


152  DYES 

completely.  The  condensation  is  carried  out  in  homogeneously 
lead-lined  stirring  autoclaves,  whilst  the  oxidation  is  done  in  wooden 
vats  provided  with  propeller  stirrers  constructed  of  ash.  The 
evaporation  is  performed  in  vacuo,  and  the  separation  of  the  well- 
crystallized  colouring  matter  is  done  by  centrifuging.  On  treating 
the  mother-liquor  with  aniline  an  impure  dye  is  formed  which 
constitutes  the  Mark  II.  of  commerce. 

More  recently  the  i:2:4~benzaldehyde  disulphonic  acid  is  often 
made  from  ^-toluene  sulphonic  chloride  instead  of  from  toluene. 
Owing  to  this  and  other  uses  for  the  substance  the  once  almost  value- 
less sulphochloride  has  risen  considerably  in  price. 

SO3C1 

Hydrolysis  with 

cone.  H2SO4 
CH3 

p -Toluene  sulphonic  p-Toluene  sulphonic  1:2:  ^-Toluene  di- 

chloride.  acid.  sulphonic  acid. 

SO.H 
Mn3O4 


i  :2 :  ^-Benzaldehyde 
disulphonic  acid. 


8.  SULPHUR   MBLTS 

Primuline  (Green)  y 

Chloramine  Yellow  FF  (Naphthamine  Yellow  NN)  and  Thiazole  Yellow, 

from  jb-Toluidine. 

Generally  speaking  sulphur  reacts  with  aromatic  amines  to  give 
substitution  products,  two  aromatic  nuclei  being  joined  together 
by  a  sulphur  atom  to  give  a  thio-compound.  A  number  of  different 
bodies  are,  however,  always  produced  simultaneously,  and  it  is  quite 
impossible  to  obtain  homogeneous  reaction  products.  Even  by 
acting  upon  ^-toluidine  with  sulphur  four  products  are  formed  which 
may  be  easily  recognized,  in  spite  of  various  views  which  have  been 
expressed  to  the  contrary.  These  are  in  the  first  place  unchanged 


SULPHUR  MELTS  153 

/>-toluidine,  then  thiotoluidine,  dehydrothiotoluidine,  and  bis- 
dehydrothiotoluidine.  The  following  formulae  indicate  the  con- 
stitution of  the  above  substances  : 


4 
V 

CH. 

p-Toluidine.      Thio-p-Toluidine.  Dehydrothio-p-Toluidine. 

I.  II. 


NH< 


"  Bis  "-dehydrothio-p-Toluidiney  or  Primuline  base. 
III. 

214  Cms.  (2  mols.)  of  />-toluidine  are  heated  with  140  gms.  214 
powdered  sulphur  (not  flowers  of  sulphur)  and  2  gms.  dehydrated 
sodium  carbonate  l  to  180°  in  a  stirring  pot  provided  with  a  reflux  2  gms 
condenser  as  shown  on  Plate  XIV.  (Fig.  36).     Hydrogen  sulphide  is  Na2CO3. 
evolved  which  is  absorbed  either  in  caustic  soda  lye  or  by  a  tower 
filled  with  moist  lumps  of  caustic  soda. 

After  about  8  hours  the  evolution  of  hydrogen  sulphide  slackens 
and  the  temperature  is  then  raised  slowly  to  220°,  and  kept  there  for 
5  hours.  There  is  practically  no  further  evolution  of  hydrogen 
sulphide,  and  the  melt  is  then  transferred  to  a  flat  tin  tray  where  it 
solidifies  to  a  light  yellow  crystalline  cake.  Yield  235  gms. 

Separation  of  the  Melt. 

Method  i. — The  cold,  hard  melt  is  finely  powdered  and  intimately 
mixed  with  i  %  of  its  weight  of  dehydrated  sodium  carbonate,  the 
purpose  of  which  is  to  prevent  the  formation  of  lumps  on  sulphona- 
tion.     100  Gms.  of  the  melt  are  added  to  300  gms.  monohydrate,   100  gms. 
the  temperature  being  allowed  to  rise  freely.     As  soon  as  all  is  in  Maltt 
solution,  which  will  occupy  about  an  hour,  the  mixture  is  cooled  Na2CO3. 
to  25°  with  continuous  stirring,  and  200  gms.  of  66  %  oleum  are   100  gms. 
allowed  to  drop  in  during  an  hour  with  good  cooling  and  stirring,  the  H^3o4. 

1  The  addition  of  soda  is  necessary  in  order  to  neutralize  the  traces  of  acidic    200  gms. 
substances  which  are  always  found  in  sulphur.     If  this  is  omitted,  dark-coloured    55j  '° 
to  black  primuline  melts  are  obtained  almost  invariably.  leum. 


500  gms. 
Ice  and 
500  gms. 
H2O. 


About  50 
gms.  20  % 
NH3  + 
800  gms. 


DYES 

temperature  being  kept  below  30°.  After  stirring  for  5  hours  at  30°, 
the  temperature  is  raised  to  40°,  and  kept  there  until  a  small  test 
portion  of  the  mixture  dissolves  readily  in  dilute  ammonia.  Complete 
solution  is  usually  attained  in  10  hours,  but  it  is  advisable  not  to 
stop  the  operation  at  this  point  as,  for  the  subsequent  filtration,  the 
mass  must  be  thoroughly  sulphonated  (cf.  also  sulphonation  of 
/3-naphthylamine  on  p.  37).  The  mixture  is  now  poured  on  to 
500  gms.  ice  and  500  c.cs.  water,  and  filtered  off  after  standing  for 
12  hours.  The  sulphonic  acid  is  thoroughly  washed  out  with  cold 
water,  by  which  means  the  greater  part  of  the  toluidine  sulphonic 
acid  and  the  thiotoluidine  sulphonic  acid  is  washed  away.  As  soon 
as  the  washings  show  only  a  faint  mineral  acid  reaction,  the  cakes  are 
dissolved  in  about  50  gms.  ammonia  (20  %  NH3)  and  800  c.cs.  water, 
the  whole  being  made  up  to  1200  c.cs.  at  80°.  The  sparingly  soluble 
ammonium  salt  of  dehydro-thiotohiidine  sulphonic  acid  separates 
out  completely  in  the  course  of  2  days,  when  it  is  filtered  and  washed 
with  a  little  5  %  ammonia.  The  mother-liquor  contains  the  Primu- 
line, which  is  precipitated  at  the  boil  with  15  %  of  common  salt. 

The  yield  of  dry  ammonium  salt  is  about  25  gms.>  and  that  of 
Primuline  about  So  gms.  of  concentrated  product. 

Method  2. — The  finely  powdered  melt  is  extracted  with  alcohol 
of  not  less  than  90  %  strength.  By  this  treatment  the  toluidine, 
thiotoluidine,  and  dehydrothiotoluidine  go  into  solution  whilst  a 
pure  Primuline  base  remains  behind.  The  alcoholic  extract  is 
evaporated  down  to  dryness,  and  the  toluidine  and  part  of  the  thio- 
toluidine are  finally  driven  off  by  heating  to  250°.  The  product  so 
obtained  is  sulphonated  with  25  %  oleum. 

Method 3.— -The  sulphonation  is  effected  as  before,  and  the  washed 
sulphonic  acid  is  dissolved  at  80°  in  twenty  times  its  volume  of  water 
and  the  necessary  quantity  of  caustic  soda  lye,  after  which  sufficient 
salt  is  added  to  give  an  8  %  solution,  and  the  whole  is  filtered  at  75°. 
The  Primuline  remains  behind,  whilst  the  dehydrothiotoluidine 
sulphonic  acid  is  dissolved  in  the  form  of  its  easily  soluble  sodium 
salt,  which  may  subsequently  be  salted  out. 

Primuline,  discovered  by  A.  G.  Green,  was  the  first  artificial 
direct  yellow  dye  which  could  be  diazotized  on  the  fibre  and  de- 
veloped by  means  of  phenols  or  amines  to  give  dyeings  fast  to  washing. 
On  treatment  with  (3-naphthol,  Primuline  Red  is  formed,  which  was 
at  one  time  made  use  of  to  a  very  large  extent.  The  fastness  to 
washing  is  good,  but  the  fastness  to  light  is  insufficient  ;  further,  it 
cannot  be  discharged  to  a  white,  but  only  to  a  yellow,  as  the  Primuline 
base  withstands  the  action  of  all  discharging  agents. 


SULPHUR  MELTS  155 

Naphthamine  Yellow  NN  (and  FF)  and  Thiazole  Yellow. 

Originally  dehydrothiotoluidine  was  a  by-product,  and  in  the 
early  days  of  Primuline  manufacture  was  melted  up  with  sulphur 
to  Primuline  base.  Nowadays  this  relationship  has  quite  altered 
as  the  originally  worthless  dehydrothiotoluidine  has  now  become  the 
chief  product.  Unfortunately  it  is  not  possible  so  to  conduct  the 
melt  that  only  the  simple  dehydrothiotoluidine  is  formed,  and  state- 
ments to  the  contrary  are  incorrect.  At  the  present  time  Primuline 
is  the  by-product,  and  is  sold  for  what  it  will  fetch.  The  dyes  which 
are  manufactured  from  dehydrothiotoluidine  are  of  various  kinds. 
The  free  base  or  its  sulphonic  acid  is  diazotized  and  then  combined 
with  various  naphthol  sulphonic  acids,  e.g.  with  the  so-called  e-acid 
(=  naphthol  disulphonic  acid  1:3:8).  This  colour  is  distinguished 
by  its  great  purity,  and  can  be  discharged  completely  to  a  pure  white. 
Direct  red  dyes  of  this  kind  come  into  the  market  under  various  names 
and  are  referred  to  usually  as  dyes  of  the  Erika  Red  type.1  Besides 
the  actual  azo  colours  derived  from  dehydrothiotoluidine,  two  other 
products  are  prepared  which  are  important  yellow  dyes.  The  first 
of  these  is  Naphthamine  Yellow  NN  or  Chloramine  Yellow  (Kalle  & 
Co.),  formed  by  oxidizing  dehydrothiotoluidine-sulphonic  acid  with 
sodium  hypochloride,  whilst  the  other  is  Thiazole  Yellow  or  Clayton 
Yellow,  which  is  produced  by  combining  diazotized  dehydrothio- 
toluidine-sulphonic acid  with  a  second  molecule  of  the  same  com- 
pound ;  by  this  means  a  diazo-amino  compound  is  formed  which  is 
further  described  below. 

It  may  also  be  noted  that  by  alkylating  Primuline  handsome 
yellow  basic  and  acid  dyes  are  formed  which  have  not,  however,  any 
great  importance. 

Naphthamine  Yellow  NN. 
Formula  : 

Dehydrothiotoluidine-)  _]Sr=M_  J  Dehydrothiotoluidine- 
sulphonic  acid.        f  J        sulphonic  acid. 

67*4  Gms.  (2/10  mol.)  of  pure  100  %  ammonium  salt  of  molecular  6?'4 
weight  337,  corresponding  to  14  gms.  sodium  nitrite,  are  dissolved  NHsa 
in  exactly  8'2  gms.  100  %  caustic  soda,  and  300  c.cs.  water,  and  the  8-2  gms 
ammonia  is  then  boiled  off,  as  even  traces  of  ammonia  upset  the  ^^ 
oxidation.      After    an    hour,    when    the    odour    of   ammonia   has  300  c.cs 

TT     S~\ 

1  Erika  Z  of  the  Berlin  Aniline  Co.  is  the  combination  :     Dehydro-thioxyli- 
dme  +  fe-acid.     Similar  dyes  are  obtained  from  naphthol  disulphonic  acid  1:3:6. 


156 


DYES 


io'5  gms. 
TOO  % 
HC1O. 


disappeared,  the  solution  is  made  up  to  500  c.cs.  at  20°,  and  is  mixed 
with  10*5  gms.  HC1O  in  the  form  of  an  approximately  5  %  sodium 
hypochlorite  solution.  Both  the  ammonium  salt  and  the  hypo- 
chlorite  must  be  exactly  determined  by  titration.  The  temperature 
rises  about  4°  and  after  i  hour  a  small  test-portion  is  heated  in  a  test- 
tube  and  salted  out.  The  precipitate  must  be  a  pure  orange,  and 
potassium-iodide-starch-paper  should  show  clearly  the  presence 
of  hypochlorous  acid.  If  this  is  not  found  to  be  the  case  a  further 
quantity  of  hypochlorite  is  added.  After  standing  for  5  hours,  the 
mixture  is  boiled  up,  precipitated  with  15  %  of  common  salt,  and 
the  product  filtered  off.  Yield  about  75  gms.  strong  dye. 

Naphthamine  Yellow  NN  is  the  fastest  to  light  of  all  yellow  cotton 
dyes,  and  is  completely  stable  towards  chlorine.  For  this  reason  it 
is  used  in  large  quantities  in  the  United  States,  where  the  washing  is 
always  treated  with  bleaching  agents.  It  is  not  so  pure  as  Chryso- 
phenine,  and  is  inferior  to  it  as  regards  strength. 


Formula 


Thiazole  Yellow  or  Clayton  Yellow. 


14  gms. 

Nitrite 

dehydro- 

thiotoluidine- 

sulphonic 

acid. 

25  gms. 

50% 

NaOH. 

25  c.cs. 

30% 
HC1. 

7  gms- 
NaN02. 

25  gms. 
Na2CO3. 
25  c.cs. 

20% 

NH3. 


Dehydrothiotoluidine- >  _^r  _XTTT_  ^  Dehydrothiotoluidine- 
sulphonic  acid.         \  ~  \        sulphonic  acid. 

An  amount  of  dehydrothiotoluidine-sulphonic  acid  corresponding 
to  14  gms.  sodium  nitrite  are  dissolved  in  25  gms.  30  %  caustic  soda, 
and  the  solution  is  divided  into  two  equal  parts,  one  of  which  is 
acidified  with  25  c.cs.  concentrated  hydrochloric  acid.  It  is  diazo- 
tized  at  10°  during  2  hours  with  7  gms.  of  100  %  sodium  nitrite. 
The  orange-yellow  diazo-compound  is  then  run  into  the  other  half 
of  the  sulphonic  acid,  to  which  a  further  25  gms.  dehydrated  sodium 
carbonate  in  a  little  water  and  25  c.cs.  strong  ammonia  have  been 
added.  The  temperature  during  the  coupling  should  be  4-5°,  and 
it  is  advisable  to  keep  the  solution  as  concentrated  as  possible.  After 
2  hours  the  liquid  is  heated  up  to  30°  and  allowed  to  stand  over-night. 
Next  day  it  is  heated  up  to  80°  and  salted  out  with  20  %  of  salt. 
The  yield  of  strong  dye  is  about  85  gms. 

Thiazole  Yellow  (Clayton  Yellow,  Mimosa,  etc.)  is,  in  contrast 
to  Chloramine  Yellow,  the  most  fugitive  yellow  in  the  whole  dye 
industry,  and  it  is  a  matter  for  surprise  that  such  a  product  should 
ever  have  been  used  at  all. 

Thiazole  Yellow  is  altered  by  caustic  soda  solution  from  a  pure 
yellow  to  a  bright  red,  for  which  reason  it  is  used  as  a  reagent  for 
caustic  alkali  (see  "  Thiazole  paper  ").  As  already  mentioned,  it  is 


SULPHUR  MELTS  157 

extremely  loose,  but  possesses  great  purity  and  strength,  so  that  it  is, 
unfortunately,  used  for  dyeing  cheap  qualities  of  textile  goods. 

On  sulphonating  colour  bases  of  the  Primuline  type  by  the  "  bake 
process,"  sulphonic  acids  are  obtained  which  form  azo  colours  faster 
to  light  than  those  prepared  from  the  ordinary  sulphonic  acid.  It  is 
assumed  that  on  "  baking  "  the  sulphonic  group  enters  in  the  ex- 
position to  the  amino  group,  by  which  means  the  fastness  to  light  is 
considerably  increased  ;  attention  has  already  been  called  to  this 
relationship  in  connection  with  the  pyrazolone  colours. 

Notes  on  Works  Technique  and  Practice. — The  preparation  of  the 
Primuline  melt  is  carried  out  in  pots  heated  in  an  oil-bath  and  pro- 
vided with  reflux  condensers  which  are  filled  with  hot  water  to  prevent 
the  ^>-toluidine  which  sublimes  from  stopping  up  the  tubes.  The 
hydrogen  sulphide  is  collected  in  caustic  soda  solution  and  used  for 
reductions.  In  the  early  days  of  the  manufacture  of  Primuline  the 
hydrogen  sulphide  was  simply  burnt  under  the  boiler,  which  is  a 
thoroughly  irrational  proceeding  and  distinctly  unpleasant  for  the 
neighbourhood.  The  extraction  with  alcohol  is  carried  out  in  iron 
boilers  provided  with  perforated  bottoms  so  that  the  alcohol  may 
be  constantly  redistilled  and  used  again  as  in  a  Soxhlet  extraction 
apparatus.  After  distilling  off  the  alcohol  from  the  extract  the 
residue  is  reheated  in  the  oil-heated  boiler  to  240°  until  toluidine 
ceases  to  be  evolved. 

Analogous  products  to  Chloramine  Yellow,  Thiazole  Yellow,  etc., 
may  also  be  prepared  from  Primuline  itself,  but  these  colours  are 
much  redder,  weaker,  and  duller  in  shade,  so  that  they  are  little  in 
demand. 


Sulphur  Black  T  from  Dinitrochlorbenzene. 
Reaction  : 

Cl  Cl 


2NO2         NaOH                 2|NO2         Na2g2        Dye  of  unknown 
— >  I  ^.  constitution. 

N02  N02 

70  Cms.  dinitrochlorbenzene  are  heated  to  90°  with  stirring  in  a   120  c.cs. 
glass  or  iron  vessel  with  120  c.cs.  of  water,  and  to  it  is  added  during  Water- 
2  hours  108  gms.  of  35  %  caustic  soda  solution,  so  that  the  reaction  DimSo- 
never  becomes  strongly  alkaline.     Heating  is  continued  until  a  test  chlorbenzene 
portion  dissolves  to  a  clear  solution  in  water,  a  further  quantity  of  3^"*' 

NaO°H. 


158  DYES 

caustic  lye  being  added  if  necessary.  The  suspension  of  the  sodium 
salt  of  dinitrophenol  is  cooled  to  45°,  and  to  it  is  added  a  solution  of 
50  gms.  S.  50  gms.  sulphur  and  125  gms.  crystalline  sodium  sulphide  in  125  gms. 
125  gms.  water.  The  temperature  is  then  raised  to  60°,  the  total  volume  being 
125  gms.  6°°  c.cs.  The  mixture  is  next  heated  cautiously  to  80°  on  the  water- 
cryst.  bath,  and  then,  in  the  course  of  2j  hours,  to  105°,  on  an  oil-bath. 

The  mass  is  now  boiled  under  a  reflux  for  30  hours  without  stirring, 
and  is  then  diluted  with  600  c.cs.  water.  After  cooling  down  to 
60°  air  is  blown  through  the  liquid  until  the  dye  is  completely  pre- 
cipitated, when  it  is  filtered  off  and  dried  at  70°.  The  yield  is  about 
70  gms.  Cotton  is  dyed  at  the  boil,  using  four  times  the  weight  of 
crystalline  sodium  sulphide  calculated  on  the  weight  of  dye. 

Notes  on  Works  Technique  and  Practice. — Sulphur  Black  T  is  the 
most  important  Sulphur  Black  on  the  market,  and  is  superior  to 
other  brands  as  regards  fastness  to  washing  and  light.  Charges  of 
500-1500  kilos,  of  dinitrochlorbenzene  are  made  use  of  in  the  works, 
the  melt-pots  having  capacities  up  to  12,000  litres  and  the  oxidizing 
vessels  up  to  30,000  litres.  With  such  large  charges  it  is  unnecessary 
to  heat  externally,  as  the  heat  of  the  reaction  suffices.  The  pots  are 
made  of  cast-iron,  and  are  rapidly  corroded.  From  the  mother- 
liquor  sodium  thiosulphate  may  be  obtained  which  is  used  in  photo- 
graphy and  in  the  textile  industries  ;  a  certain  portion  is  also  used  in 
the  dye-works  for  the  production  of  Methylene  Blue.  The  price  of 
Sulphur  Black  T  was  formerly  about  80-90  centimes  per  kilo,  for  a 
35  %  product,  so  that  only  those  colour  factories  can  make  it  success- 
fully which  are  careful  to  use  up  all  by-products.  Further,  those 
colour  factories  which  do  not  manufacture  chlorbenzene  and  dinitro- 
benzene  are  practically  out  of  the  running. 


SULPHUR  MELTS 


Auramine  OO 

(according  to  Traugott  Sandmeyer).1 

Reaction :  N(CH3)2 


N(CH3)2.HC1 

6.. 

Dimethylaniline . 


0 


+CH20 

Formaldehyde. 


CH9       +S+NH4C1 

2    +NH3+[NaCl]-> 


N(CH3) 


\ 


C  :  NH2 


0 


.  N(CH3)2  . 


Tetramethyl-diamino-diphenylmethane.  Auramine  OO. 

(a)  Tetramethyl-diamino-diphenylmethane. 

242  Gms.  of  pure  dimethyl  aniline  are  mixed  with  140  c.cs.  of 
water  and  260  gms.  of  hydrochloric  acid  (30  %),  and  to  it  is  added 
at  30°,  60  gms.  of  40  %  formaldehyde,  the  strength  of  which  has  been 
accurately  determined  beforehand  by  titration.  The  ratio  of  formal- 
dehyde to  dimethylaniline  is  ri:  2  molecules. 

The  mixture  is  heated  up  to  85°,  with  occasional  stirring,  for 
5  hours,  and  the  base  precipitated  with  about  120  gms.  of  soda 
dissolved  in  a  little  water.  The  product  is  filtered  off  at  20°  and  is 
thoroughly  washed  with  water.  As  the  melting  point  is  90°,  the 
drying  temperature  should  not  exceed  60°.  Yield  about  255  gms., 
i.e.  practically  quantitative. 


242  gms. 
Pure  di- 
methyl- 
aniline. 
260  gms, 
30%  HC1. 
140  gms. 
H2O. 
60  gms. 
40  % 
CH2O. 
About 
1 20  gms. 
Na2C03. 


(b)  Auramine  OO. 
12 7  Gms.  diamino  base,  32  gms.  sulphur,  70  gms.  ammonium  127  gms. 


base. 
32  gms. 
70  gms. 


chloride,  and  1000  gms.  common  salt  are  heated  up  to  110°  in  a 
stirring-pot  similar  to  that  shown  on  Plate  XIV.,  Fig.  36.     It  is 
essential  that  all  the  substances  should  be  finely  divided  and  should  NH4C1. 
contain  no  water.     The  temperature  is  raised  to  130°  during  2  hours,2 

1  In  the  patent  literature  Auramine  is  connected  with  the  meaningless  name 
of  Peer.      The  true  discoverer  was  Sandmeyer,  whose  name  was  lost  sight  of  owing 
to  the  heated  controversy  as  to  the  ownership  of  the  colour. 

2  Oil-bath  about  25°  higher, 


160  DYES 

-f-NH3.  a  rapid  stream  of  dry  ammonia  being  passed  into  the  apparatus  from  a 

cylinder.  Any  moisture  is  carried  away  by  the  gas,  and  at  about 
140°  a  vigorous  evolution  of  hydrogen  sulphide  begins,-  which  lasts 
from  5-7  hours,  according  to  the  speed  of  the  stream  of  ammonia. 
The  temperature  is  raised  to  145°  during  5  hours,  the  stirring  being 
continued,  and  the  hydrogen  sulphide  absorbed  in  concentrated 
caustic  soda  lye.  It  is  also  advisable  to  keep  up  a  slight  excess 
pressure  of  about  1/5  atms.,  measured  by  a  manometer,  by  throttling 
down  the  exit  tube.  The  speed  of  the  ammonia  stream  should  be 
about  5  bubbles  per  second.  Before  use  the  ammonia  must  be 
passed  through  a  wash  bottle  containing  50  %  potash,  and  then 
through  two  towers  filled  with  lumps  of  caustic  soda.1 

When  the  evolution  of  hydrogen  sulphide  has  ceased,  the  autoclave 
is  opened  and  the  brownish-yellow  powdery  mass  is  put  into  a  large 

3  litres  H2O.  porcelain  basin.  The  powder  is  covered  with  3  litres  of  water  to 
dissolve  out  the  salt,  after  which  the  dye  is  filtered  off  and  dissolved 
in  i  J  litres  of  water  at  60°.  The  temperature  must  not  exceed  this, 
as  Auramine  readily  decomposes.  The  solution  is  filtered  from  the 
residue,  consisting  of  a  little  sulphur  and  some  Michler's  ketone, 
and  the  filtrate  is  mixed  with  a  litre  of  the  salt  solution  previously 
obtained,  the  Auramine  coming  down  in  beautiful,  glistening,  golden 
leaflets.  The  yield  of  pure  dry  colour  may  reach  175  gms.  It  dyes 
cotton  mordanted  with  tannin  and  tartar  emetic  a  pure  yellow. 

Notes  on  Works  Technique  and  Practice. — Auramine  is  the  most 
important  basic  yellow  dye,  and  is  much  valued  owing  to  its  extremely 
pure  shade.  The  manufacture  is  carried  out  in  oil-jacketed  boilers 
which  must  be  very  accurately  heated,  as  the  slightest  variation 
diminishes  the  yield.  Use  is  also  made  of  Frederking  autoclaves, 
which  can  be  very  carefully  regulated.  Plate  VIII.,  Fig.  24,  shows 
such  a  flat  Auramine  pot  with  modern  steam  heating.  The  purity 
of  the  salt  used  has  a  very  considerable  influence  ;  traces  of  the 
chlorides  of  calcium  or  magnesium,  which  are  present  in  all  ordinary 
"salt,  have  an  injurious  effect.  The  best  salt  is  Galician  rock-salt, 
which  is  almost  chemically  pure.  The  ammonia  is  dried  in  small 
towers  filled  with  caustic  soda.  Only  sufficient  ammonia  is  added 
to  give  an  excess  pressure  of  half  an  atmosphere,  and  the  gas  is  then 
circulated  over  the  salt  mixture  by  means  of  a  pump.  The  hydrogen 
sulphide  is  absorbed  and  is  used  for  reductions  in  the  form  of  sodium 
sulphide.  When  the  operation  is  properly  conducted  the  yield  may 
be  up  to  132  %,  i.e.  132  kilos,  of  pure  100  %  Auramine  may  be 

1  Ammonia  cannot,  of  course,  be  dried  With  calcium  chloride,  as  all  amines 
combine  with  it. 


MISCELLANEOUS    DYES  161 

obtained  from  100  kilos,  of  tetramethyl-diamino-diphenylmethane. 
It  is  difficult  to  estimate  the  yield  as  very  few  people  are  able  to 
determine  exactly  the  precise  strength  of  dyeings  on  tannined  cotton. 
For  this  reason  it  is  usual  to  estimate  this  dye  by  titrating  with  titanous 
chloride  of  known  strength  until  a  weighed  portion  is  rendered 
colourless,  rather  than  by  dyeing  trials. 

In  addition  to  Auramine  OO,  Auramine  G  is  also  prepared  from 
monomethyl-0-toluidine  ;  it  is  purer  and  greener  than  the  OO  brand. 
The  product  from  diethylaniline  is  not  made  as  it  comes  out  in  such 
a  resinous  form  on  salting  out  that  it  is  impossible  to  work  it  up. 

Auramine  is  used  on  a  very  large  scale  for  dyeing  cotton,  and 
more  especially  paper.  The  Swedish  match  factories  alone  use  about 
eight  waggon-loads  a  year  for  dyeing  yellow  match-boxes. 


9.   MISCELLANEOUS  DYBS 

Indigo 
(Traugott  Sandmeyer's  Method).1 

Although  Sandmeyer's  Indigo  synthesis  is  no  longer  worked,  it 
affords  such  a  classical  example  of  the  co-operation  between  science 
and  technology  that  an  account  of  it  cannot  be  excluded  from  this 
book.  This  synthesis  is  one  of  the  most  remarkable  achievements 
in  the  whole  domain  of  dye  chemistry,  and  may  he  compared  with 
Leblanc's  process  for  the  manufacture  of  soda.  Like  the  latter,  it 
has  exerted  a  fertilizing  influence  on  the  whole  subject,  and  one 
portion  of  the  process  is  still  utilized  for  the  production  of  isatin 
and  its  derivatives  ;  these  relationships  will  be  discussed  later. 

Before  describing  the  individual  operations,  the  chemical 
mechanism  of  the  reactions  must  be  examined. 

(a)  Aniline  is  converted  into  A.  W.  Hoffmann's  "  thiocarbanilide" 
by  heating  with  carbon  bisulphide  : 


cs,        „   B 

CS.NH— ^      \  +  H9S 


Thiocarbanilide  (m.p.  151°) 
(A.  W.  Hoffmann). 

1  See,  also,  Sandmeyer,  Zeitschrift  fur   Farben-  und   Textil-Chemie,  1903,  7, 
129  ;  and  Helvetica  Chimica  Acta,  vol.  ii.,  234  (1919). 


II 


1 62  DYES 

(b)  The  sulphur  is  removed  from  the  Thiocarbanilide  by  means  of 
basic  lead  carbonate,  and  at  the  same  time  hydrocyanic  acid  is  added 
on,  leading  to  the  formation  of  Laubenheimer's  "  hydrocyancarbo- 
diphenylimide ' '  : 

HCN— H2S 

M.p.  137' 


N 

Hydrocyancarbodiphenylimide  (Laubenheimer) . 

(c)  The  hydrocyancarbodiphenylimide  is  converted  by  means 
of  yellow  ammonium  sulphide  into  the  thio-oxamide-diphenyl- 
amidine,  or  more  simply  "  thioamide  "  : 

H's  u  i 

\    /  / — \ 

M.p.  161-162°. 


(d)  Under   the'  influence    of   concentrated    sulphuric    acid   the 
thioamide  is  concerted  readily  into  a-isatin-anilide  : 

+  H2S04(conc.) 


a-Isatin-anilide.     M.p.  126°. 

(e)  The  a-isatin-anilide  may  be  converted  into  Indigo  in  various 
ways  ;  it  is  either  reduced  in  alcoholic  solution  with  dilute  am- 
monium sulphide,  or  it  is  converted  into  the  a-thio-isatin,  which 
yields  Indigo  at  once  with  alkalis.  The  last  method  has  been  chosen 
here  as  this  was  the  process  formerly  made  use  of  in  the  industry  : 

+  H2S     (/\~      -NH 

>     I     /'  A     c     4-   Aniline 

^/\co/L= 

a-Thio-isatin, 


MISCELLANEOUS   DYES  163 


(a)  Thiocarbanilide. 

1  86  Gms.  pure  aniline  are  boiled  up  with  100  gms.  of  pure  carbon  186  gms. 
bisulphide  until  the  evolution  of  hydrogen  sulphide  ceases,  which  Amlme- 
takes  about  2  days.     The  temperature  of  the  oil-bath  is  then  raised  cs^f" 
to    1  60°,   and   the   excess   of  bisulphide   distilled   off.     The   fused 
thiocarbanilide    is   poured  on    to  a  flat  tray  to  cool,  and  is  then 
powdered.     It  is  sufficiently  pure  for  further  treatment,  but  may 
be  obtained  chemically  pure  by  recrystallizing  from  three  times  its 
weight  of  alcohol  .     The  yield  is  about  230  gms  .     M  .p  .  1  5  1  °  . 

(b)  Hydrocyancarbodiphenylimide. 

350  Gms.  lead  nitrate,  dissolved  in  a  litre  of  hot  water,  are  carefully  350  gms. 
precipitated  at  95°  with  about  120  gms.  dehydrated  sodium  carbonate  Pb(NO3)2. 
and  the  precipitate  is  thoroughly  washed  with  water.     The  moist   I20  gms. 
basic  lead  carbonate  is  mixed  with  600  gms.  of  90  %  alcohol  in  a  Na2CO3. 
2-litre    bolt-head    provided    with    a    stirrer    and    reflux    condenser  Alcohof 
(Fig.  9),  and  is  stirred  up  to  a  completely  homogeneous  paste  ;    to 
it  is  then  quickly  added  228  gms.  (i  mol.)  of  very  finely  powdered  228  gms. 
thiocarbanilide,  and  at  25°  about  60  gms.  of  commercial  sodium  ^jj^" 
cyanide  (—1*3  mol.).1    The  temperature  of  the  mixture  must  be  60  gms. 
raised  during  an  hour  to  70°  with  vigorous  stirring,  and  a  small  N*CN. 
test-portion  is  then  filtered  off.     The  colourless  solution  should  no 
longer  blacken  a  pinch  of  basic  lead  carbonate.     If  this  is  not  the 
case,  heating  must  be  continued  for  a  further  hour  and  the  test  again 
applied  ;    if  complete  desulphurization  has  still  not  been  effected  a 
little  more  lead  carbonate  and  sodium  cyanide  may  be  added,  but 
if  the  correct  amounts  of  the  reagents  have  been  taken  no  further 
addition  will  be  necessary. 

As  soon  as  the  sulphur  reaction  is  no  longer  given  the  mixture  is 
heated  up  to  boiling,  and  the  hot  solution  is  filtered  off.  The  residue 
is  extracted  twice  more  with  half  a  litre  of  alcohol,  and  the  hydro- 
cyancarbodiphenylimide  allowed  to  crystallize  out.  The  first 
fraction  is  quite  pure,  and  weighs  about  160  gms.  After  evaporating 
down  the  mother-liquor,  a  further  4.0  gms.  of  practically  pure  product 

1   The  HCN  content  of  the  sodium  cyanide  must  be  determined. 


164 


DYES 


is  obtained.  The  yield  is  about  98  %.  The  hydrocyancarbo- 
diphenylimide  crystallizes  in  fine  yellowish 'prisms,  having  a  melting 
point  of  137°.  The  mother-liquors  contain  prussic  acid,  and  must 
be  handled  with  due  care. 


200  gms. 
Hydrocyan- 
carbodi- 
phenylimide. 


460  gms. 

20% 

NH3. 

25  gms.  S. 


200  gms. 
Thioamide. 
800  gms. 
66°  Be. 
H2SO4. 


i  litre  H2O. 
i  kg.  Ice. 


(c)  "  Thtoamide." 

The  addition  of  hydrogen  sulphide  to  the  hydrocyancarbo- 
diphenylimide  takes  place  readily  if  it  is  very  finely  powdered,  for 
which  reason  it  is  necessary  to  convert  the  product  into  the  desired 
form  either  by  grinding  or  by  sifting.  200  Gms.  hydrocyancarbo- 
diphenylimide  are  emulsified  with  500  gms.  yellow  ammonium 
sulphide  solution  at  35°  by  vigorous  stirring.  The  ammonium 
sulphide  solution  is  prepared  by  passing  35  gms.  hydrogen  sulphide 
into  a  suspension  of  25  gms.  powdered  sulphur  in  460  gms.  of 
20  %  ammonia.  If  the  hydrocyancarbodiphenylimide  has  been 
powdered  sufficiently,  the  hydrogen  sulphide  adds  on  quantitatively 
within  12  hours,  which  may  be  recognized  by  the  fact  that  a  washed 
test-portion  of  the  product  dissolves  in  dilute  hydrochloric  acid. 
It  is  then  filtered  off  and  thoroughly  washed  with  water  ;  the  product 
is  sufficiently  pure  for  the  next  stage.  Yield  about  220  gms.  It 
crystallizes  from  alcohol  in  yellow  prisms  having  a  melting  point  of 
162°. 

(d)  a-Isatin-anilide. 

The  ring-formation  giving  isatin  derivatives  only  occurs  under 
certain  very  definite  conditions  ;  it  is  important  that  hot  sulphuric 
acid  be  used. 

200  Gms.  of  finely  divided  drythioamide  are  added  during  a  quarter 
of  an  hour  to  800  gms.  of  94  %  sulphuric  acid,  at  exactly  94°  ;  the 
mixture  heats  up  fairly  strongly  and  must  be  cooled.  As  soon  as  all 
has  been  added  the  mixture  is  heated  for  a  further  hour  to  106-108°, 
after  which  time  the  evolution  of  SO2  will  have  ceased.  The 
solution  is  cooled  down  to  20°  and  is  converted  directly  into  the 
hydrochloride  of  a-isatin-anilide  by  pouring  in  a  thin  stream  into 
a  mixture  of  i  litre  water,  2  kilos,  ice,  and  500  gms.  salt,  stirring  being 
continued  without  interruption.  The  hydrochloride  of  isatin- 
anilide  separates  out,  mixed  with  finely  divided  sulphur,  as  a  light 
reddish-brown  precipitate. 

To  obtain  the  anilide  in  a  pure  form  it  is  filtered  off  and  thoroughly 
washed  with  20  %  salt  solution.  The  hydrochloride  freed  from  all 
acid  is  then  stirred  up  with  water  and  dilute  sodium  carbonate  solution 


MISCELLANEOUS   DYES 


165 


until  there  is  a  faintly  alkaline  reaction.  The  precipitate  of  anilide 
and  sulphur  is  filtered  off,  thoroughly  washed,  and  the  dried  mixture 
extracted  with  cold  carbon  bisulphide.  Finally,  the  anilide  is 
crystallized  from  hot  alcohol,  from  which  it  is  obtained  in  the  form 
of  dark  needles  having  a  melting  point  of  126°,  the  yield  from  200  gms. 
thioamide  being  about  150  gms.  pure  substance.  On  boiling  with  a 
slight  excess  of  dilute  hydrochloric  acid,  the  anilido  group  is  split 
off  as  aniline,  pure  isatin  being  precipitated  directly.  M.p.  200-201°. 
It  is  recrystallized  from  hot  water  in  which  it  is  easily  soluble. 
Isatin  is  an  important  intermediate  for  the  synthesis  of  various 
valuable  vat-colours.  Of  particular  importance  are  those  vat-dyes 
obtained  from  a-isatin-anilide  by  condensing  with  /3-hydroxy- 
thionaphthene  (Thioindoxyl).  G.  Engi  was  the  first  to  notice  that 
quite  different  dyes  are  obtained  according  to  whether  isatin  itself 
be  used  or  its  anilide.  Isatin  condenses  by  exchanging  the  /3-oxygen 
atom  whilst  the  anilide,  curiously  enough,  splits  off  the  aniline  and 
gives  a-condensation  products.  The  a-condensation  products  are 
much  more  valuable  than  the  isomers. 


From  Isatin  : 


NH 


\/\/CO(a) 


C 

CO   S 

\ 


Thioindigo  Scarlet  R 

(Kalle). 
Ciba  Red  G  =  Dibrom 

derivative. 


From  a-Isatin-anilide : 


NH     S /\ 

i          i 

\/crrc\A/ 

CO  (a>        CO 

(13) 


Ciba  Violet  B   -Tribrom 
derivative. 

Ciba  Violet  38  =  Dibrom 

derivative. 

Ciba  Grey  G    =Monobrom 
derivative. 


(e)  oi-Thioisatin  and  Indigo. 

In  order  to  obtain  Indigo  from  the  solution  of  isatin-anilide  in 
sulphuric  acid  it  is  not  necessary  to  isolate  either  the  pure  anilide 
or  the  hydrochloride,  but  the  thioisatin  may  be  obtained  directly 
from  the  solution.  A  solution  of  sodium  hydrosulphide  is  prepared 


1 66 


DYES 


45  grns. 

NaOH 

+H2S. 


6  litres 
Ice + water. 


About 
30  gms. 
Na2C03. 


by  passing  hydrogen  sulphide  into  a  solution  of  45  gms.  caustic 
soda  dissolved  in  150  c.cs.  of  water.  This  is  then  mixed  with  the 
sulphuric  acid  solution  of  isatin-a-anilide,  from  200  gms.  thioamide, 
by  allowing  both  to  run  simultaneously  into  6  litres  of  ice-water.  A 
slight  but  distinct  excess  of  sulphuretted  hydrogen  should  always 
be  present.  The  reduction  occupies  about  half  an  hour,  and 
the  thioisatin  separates  out  as  a  voluminous  brown  precipitate, 
aniline  sulphate  remaining  behind  in  the  solution.  The  thioisatin 
is  filtered  off  as  soon  as  a  filtered  test-portion  of  the  liquid  gives  no 
further  precipitate  on  treatment  with  sodium  sulphide,  which  will 
be  the  case  after  about  an  hour.  The  precipitate  is  then  washed 
until  the  mother-liquor  has  a  specific  gravity  of  only  1*007 
(i°  Be).  The  washed  precipitate  is  stirred  up  with  3  litres  of  water 
to  which  concentrated  sodium  carbonate  solution  is  added  until  the 
reaction  becomes  strongly  alkaline,  about  30  gms.  soda  being  required 
for  this  purpose.  The  formation  of  Indigo  takes  place  very  rapidly, 
and  the  mixture  is  preferably  warmed  for  one  hour  at  60°,  and  is 
then  left  stirring  over-night.  Next  day  the  Indigo  and  sulphur 
are  filtered  off,  thoroughly  washed,  and  dried  at  80°.  The  dried 
colouring  matter  is  then  extracted  with  twice  its  weight  of  carbon 
disulphide,  80  gms.  pure  Indigo  being  obtained. 

Notes  on  Works  Technique  and  Practice. — The  reactions  involved 
in  the  Sandmeyer  synthesis  go  surprisingly  smoothly,  the  yield 
of  dye  calculated  upon  the  aniline  taken  being  about  80  %  of  that 
theoretically  possible.  The  process  was  used  for  a  short  time  by 
J.  R.  Geigy,  the  cost  of  production  being  io'8  francs  per  kilogram  of 
100  %  product.  Indigo  prepared  by  the  Sandmeyer  method  vats 
better  than  any  other  artificial  product,  and  was  immediately 
welcomed  by  dyers.  It  was  found  to  be  possible  to  effect  the  entire 
manufacture  without  the  use  of  a  drop  of  alcohol,  since  all  the  sub- 
stances involved  react  readily  in  aqueous  solution  if  sufficiently  finely 
divided.  The  chief  difficulty  is  not  the  hydrocyanic  acid,  but  the 
hydrogen  sulphide,  which  is  a  dangerous  industrial  poison,  as, 
after  a  short  time,  it  can  no  longer  be  smelt.  The  lead  sulphide  may  be 
split  up  by  means  of  concentrated  hydrochloric  acid  into  lead  chloride 
and  hydrogen  sulphide,  the  latter  being  returned  to  the  process. 
Soon  after  the  introduction  of  this  promising  method  of  manufacture 
it  was  displaced  by  the  process  of  the  Deutsche  Gold-und-Silber- 
scheide  Anstalt,  as.  in  this  latter  method  the  yields  were  also  increased 
to  about  85  %  by  the  latest  improvements  so  that  effective  competition 
was  no  longer  possible.  At  the  same  time  it  is  always  con- 
ceivable that  under  favourable  conditions  the  Sandmeyer  process 


MISCELLANEOUS    DYES  167 

may  again  become  of  importance.  Since  the  discovery  by  Frasch 
of  the  great  sulphur  deposits  in  Louisiana  and  the  electro-thermal 
preparation  of  sodium  cyanide  and  carbon  disulphide  this  possibility 
must  always  be  borne  in  mind. 


Alizarin  from  Pure  Anthraquinone. 

Reaction  : 


2-  Anthraquinone  Sulphonic  Acid. 

CO      OH  CO       °H 


co 

i  \2-Hydroxyanthraquinone  Sulphonic  Acid.  Alizarin. 

(a)  2-  Anthraquinone  Monosulphonic  Acid  Sodium  Salt 
(Silver  Salt). 

On  treating  anthraquinone  with  fuming  sulphuric  acid  two 
sulphonic  groups  readily  enter  the  nucleus  so  that  it  is  necessary  to 
reduce  the  quantity  of  SO3  to  such  an  extent  that  a  fairly  large  portion 
of  the  anthraquinone  remains  unchanged. 

100  Gms.  of  dry  finely  divided  anthraquinone  are  added  cautiously  100  gms 
to  150  gms.  of  oleum  containing  25  gms.  of  SO3.     The  temperature  q^J^e 
must  not  exceed  30°,  and  stirring  must  be  continued  without  inter-   i50  gms 
ruption  in  order  to  prevent  any  local  overheating.     The  temperature  £5  % 
is  raised  during  4  hours  to  120°  by  means  of  an  oil-bath,  and  after  a 
further  2  hours  to  140°.     The  vessel  must  be  kept  well  closed  to 
prevent  SO3  from  distilling  off  (see  Fig.  4).     After  cooling,  the 
mixture  is  poured  into  3  litres  of  water  and  the  unchanged  anthra- 
quinone filtered  off.     Some  25-40  gms.  are  recovered,  according  to 
the  manner  in  which  the  sulphonation  has  been  effected.     The 
sulphuric  acid  solution  is  now  completely  neutralized  by  means  of 
chalk  or  limestone  as  described  on  p.  15,  and  the  calcium  sulphate  About 
filtered   off.     The   lime   is   then   precipitated   with   dilute   sodium 
carbonate  until  a  filtered  test-portion  gives  no  further  precipitate 


1 68 


DYES 


with  soda.  The  filtered  solution  is  evaporated  down  to  400  c.cs. 
over  a  gas-ring,  and  is  then  allowed  to  cool.  The  sodium  salt  of 
the  anthraquinone-2-sulphonic  acid  separates  out  in  the  course  of  a 
couple  of  days  as  a  glistening,  silvery  precipitate.  It  is  filtered  off 
and  washed  with  a  little  water.  The  yield  of  dry  substance  is  60-90  gms . 
A  few  grams  of  less  pure  substance  may  be  recovered  from  the 
mother-liquor,  but  always  contain  a  little  disulphonic  acid,  no  matter 
how  carefully  the  sulphonation  is  carried  out. 

It  is  also  possible  to  avoid  liming-out,  as  is  usually  done 
technically,  by  pouring  the  sulphonation  product  into  a  litre  of 
water,  filtering  from  unchanged  anthraquinone  after  standing  for  an 
hour,  and  then  salting  out  with  20  %  of  common  salt.  The  pre- 
cipitated sodium  salt  is  filtered  off,  washed  with  a  little  concentrated 
brine,  and  pressed.  It  is  then  pure  enough  for  the  melt.  With 
proper  working  the  mother-liquors  contain  only  2-2|  %  of  di- 
sulphonic acids,  which  may  be  rejected.  In  the  works  rather  more 
concentrated  oleum  is  used,  about  40  %,  as.  in  this  case  there  is  less 
danger  of  over-sulphonating. 


100  gms. 
Silver  salt. 
(ioo  %). 
260  gms. 
NaOH. 
28  gms. 
NaClO3. 


(b)  The  Alizarin  Melt. 

The  alizarin  melt  was  first  introduced  into  chemical  technology 
by  Caro,  and  the  addition  of  an  oxidizing  agent,  saltpetre,  was  first 
made  use  of  by  the  Society  of  Chemical  Industry  in  Basle.  At  the 
beginning  of  the  'seventies  chlorates  were  made  use  of,  following  the 
suggestion  of  Koch,  and  at  the  present  day  only  the  cheap  electrolytic 
sodium  chlorate  is  utilized. 

ioo  Gms.  of  ioo  %  silver  salt  are  heated  with  260  gms.  ioo  % 
caustic  soda,  28  gms.  sodium  chlorate,  and  sufficient  water  to  make 
the  total  volume  up  to  670  c.cs.,  the  mixture  being  heated  up  with 
continuous  stirring  in  an  autoclave  to  185°,  the  pressure  attaining 
5-6  atmospheres.  After  48  hours  the  melt  is  allowed  to  cool,  and  is 
then  examined  to  see  if  it  is  finished.  For  this  purpose  2  c.cs.  of  the 
melt  are  taken,  the  Alizarin  precipitated  with  the  requisite  quantity 
of  concentrated  hydrochloric  acid,  and  the  filtrate  extracted  twice 
with  a  little  ether.  The  liquid,  from  which  all  Alizarin  has  been 
removed,  is  now  diluted  to  15  c.c.,  and  the  fluorescence  observed, 
which  is  due  to  unchanged  silver  salt  or  to  monohydroxyanthra- 
quinone  sulphonic  acid.  Only  a  very  faint  fluorescence  should  be 
observable,  or  none  at  all,  and  if  necessary  the  melt  is  heated  up 
again  to  190°  for  24  hours.  The  product  is  then  diluted  with 
2  litres  of  water  and  the  Alizarin  precipitated  at  the  boil  with  50  % 


MISCELLANEOUS   DYES  169 

sulphuric  acid  ;  after  filtering  off  at  50°  it  is  washed  until  the  mother- 
liquor  is  free  from  salt.  The  Alizarin  is  not  dried,  as  when  once  dry 
it  no  longer  dyes  properly.  The  yield  is  estimated  by  determining 
the  moisture  and  by  test- dyeings.  Usually  the  finished  product 
contains  20  %  of  colouring  matter. 

About  70  gms.  pure  Alizarin  are  obtained  from  100  gms.  of  pure 
silver  salt. 

Notes  on  Works  Technique  and  Practice. — Next  to  Indigo,  Alizarin 
is  the  most  important  product  produced  by  the  colour  factories. 
Owing  to  its  low  price  it  is  now  made  only  at  a  few  works,  but  on  a 
very  large  scale.  The  sulphonation  is  effected  in  apparatus  of  the 
usual  type,  but  the  melts  are  being  carried  out  more  and  more 
frequently  in  Frederking  apparatus  such  as  was  shown  on  Plate  VIII. 
(Fig.  23).  As  the  chlorate  melt  attacks  the  apparatus  very  vigorously, 
a  liner  of  alkali-resistant  cast-iron  is  always  used,  which  may  be 
replaced.  There  are  many  different  forms  of  such  apparatus.  On 
the  works  scale  very  large  charges  are  used,  so  that  as  much  as 
2000-2500  kilos.  100  %  Alizarin  may  be  obtained  at  one  operation 
in  one  pot  ;  the  dye  is  then  made  up  to  1 6  %  or  20  %  paste,  the 
standardizing  being  done  by  determining  the  moisture  content,  and 
by  dye-trials.  Again  it  is  possible  technically  to  work  with  much  less 
caustic  soda,  only  no  %  of  the  theoretical  quantity  being  required, 
corresponding  to  40  gms.  instead  of  260  gms.  in  the  present  case. 
Alizarin  which  has  been  dried  may  be  reconverted  into  a  form  suit- 
able for  dyeing  by  dissolving  in  borax  and  reprecipitating  with  acetic 
acid  or  sulphuric  acid.  Dyes  of  the  alizarin  type  must,  owing  to 
their  sparing  solubility,  be  precipitated  at  the  boil,  as  only  in  this 
manner  can  they  be  obtained  in  a  suitably  fine  state  of  subdivision 
(cf.  also  Anthracene  Brown).  The  world's  production  of  100  % 
Alizarin  was  about  2,800,000  kilos.,  of  which  the  Badische  Anilin 
and  Soda  Fabrik  alone  produced  2,000,000  kilos.  For  the  Oriental 
market  a  solid  preparation  is  made  by  adding  sufficient  starch  to  the 
dye  to  convert  it  into  dry  lumps  which  swell  up  to  a  paste  on  boiling 
with  water,  and  dye  easily.  (For  dyeing  with  Alizarin,  see  the 
pattern  cards  issued  by  the  various  firms,  and  Gnehm's  "  Taschen- 
buch.") 


1 7o 


DYES 


36*6  gms. 
Benzoic 
acid. 
300  gms. 
ioo  % 
H2S04. 
50  gms. 
Gallic  acid. 


Anthracene  Brown   FF  from   Benzoic  Acid  and  Gallic 

Acid. 
Reaction  : 


OH 


CO 


°H 


OH 


i  '.Z'.^-Trihydroxyanthraquinone, 
Anthracene  Brown  or  AnthragalloL 

36*6  Gms.  (3/10  mol.)  pure  benzoic  acid  are  dissolved  in  300  gms. 
sulphuric  monohydrate  contained  in  a  glass,  porcelain,  or  iron 
beaker,  and  stirred  until  complete  solution  is  effected.  It  is  then 
heated  up  slowly  to  90°,  at  which,  temperature  50  gms.  pure  dry 
gallic  acid  (dried  at  110°)  are  added  in  small  portions  during  an  hour. 
The  temperature  is  kept  at  118°  for  6  hours,  and  then  the  melt  is 
allowed  to  drop  very  cautiously  into  a  litre  of  boiling  water  with 
continuous  stirring.  The  product  is  filtered  off  from  the  absolutely 
boiling  liquid  into  a  previously  warmed  jar,  and  the  dye  is  well 
washed  with  hot  water.  The  excess  of  benzoic  acid  crystallizes 
out  in  a  pure  form  in  a  short  time  from  the  mother-liquor.  After 
stirring  up  with  water  to  20  %  paste  the  dye  is  ready  for  use.  The 
dyeing  is  effected  upon  chrome-mordanted  wool,  chromium  fluoride 
giving  the  handsomest  and  fullest  shades. 

Notes  on  Works  Practice. — The  most  important  factor  in  this 
manufacture  is  the  absolute  purity  of  the  gallic  acid  used.  No 
"  second-quality  "  crystals  may  be  used  as  these  probably  contain 
homologues  of  gallic  acid  which  cause  troublesome  foaming  during 
the  condensation,  and  diminish  the  yield  to  50  %.  On  the  works 
also  the  boiling  liquids  are  filtered  through  filter-presses  made  of 
pitch-pine  and  provided  with  nitre-filters.  These  latter  will  last 
out  about  50  operations,  but  must  of  course  be  very  carefully  manu- 
factured if  they  are  to  meet  these  exacting  demands. 

For  the  production  of  Anthracene  Brown  for  printing  (F.  D.=fiir 
Druck)  the  process  is  very  similar.  The  condensation,  however,  is 
carried  out  at  130-140°  instead  of  at  1 18°.  The  product  obtained  by 
precipitating  in  boiling  water  is  not  sufficiently  finely  divided,  but 
gives  a  mottled  effect  on  printing.  It  is  therefore  necessary,  after 
washing,  to  convert  the  product,  as  a  10  %  suspension,  into  the  sodium 
salt  by  means  of  soda  at  80-90°,  and  then  to  precipitate  cautiously 
with  hydrochloric  acid.  After  filtering  off  again,  the  product  is 


MISCELLANEOUS   DYES  171 

made  up  to  the  desired  strength  in  a  Werner  and  Pfleiderer  mixer 
What  was  said  before  as  to  the  purity  of  the  gallic  acid  applies  still 
more  forcibly  in  the  present  case. 

A  good  quality  gallic  acid  may  be  easily  prepared  by  hydrolysing 
tannin  at  70°  in  concentrated  solution  with  caustic  soda  lye  of  at 
least  40  %.1  In  order  to  protect  the  gallic  acid  from  oxidation  a 
little  sodium  bisulphite  is  added.  The  gallic  acid  is  precipitated  with 
concentrated  hydrochloric  acid  (sulphuric  acid  must  not  be  used), 
and  is  then  crystallized  from  boiling  water. 


Gallamine  Blue  from  Gallamide. 

By  heating  nitroso-dialkyl amines  with  gallic  acid  or  its  amide, 
\vell-defmed  compounds  are  obtained  which  are  termed  Oxazines, 
The  gallic  acid  is  obtained  exclusively  from  natural  tannin. 

Reaction  :  2 


,NO 


(CH3)2NX  HO 

HC1 


CONH. 


i 

r. 


(CH3)2N 


CONH2 

N\    A 

\/l  \ 

Cl 


OH 

p-Nitrosodimethylaniline.  Gallamide.  Gallamine  Blue  (R.  Geigy). 

(a)  Nitroso-dimethylaniline. 

100  Gms.  dimethyl  aniline  are  mixed  with  200  gms.  30  %  hydro-  100  gms 
chloric  acid  and,  after  cooling,  300  gms.  of  ice  are  added.  A  concen- 
trated solution  of  60  gms.  of  100  %  sodium  nitrite  are  then  dropped  in  200 
during  5  hours,  the  beaker  being  placed  in  ice-water.  It  is  not  HC1- 
possible  to  test  for  free  nitrous  acid  with  nitrite  paper,  as  nitroso- 
dimethylaniline  hydrochloride  itself  reacts  with  it.  The  excess,  60  gms. 
therefore,  can  only  be  recognized  by  its  odour.  The  reaction  to 
Congo  paper  should,  of  course,  be  shown  the  whole  time.  After 
standing  for  6  hours,  the  product  is  filtered  off,  rinsed 'out  into  the 
filter  by  means  of  the  mother-liquor,  and  the  precipitate  sucked  as 
dry  as  possible.  Finally,  it  is  squeezed  in  a  screw-press,  and  the  moist 
nitroso-dimethylaniline  powdered  as  much  as  possible.  The  salt 

1  The  caustic  lye  must  be  free  from  chlorate  so  that  electrolytic  caustic  cannot 
be  used  or  else  oxidation  occurs  on  hydrolysis  and  acidification. 

2  One  molecule  of  nitroso-dimethylaniline  is  used  up  as  the  oxidizing  agent. 


172 


DYES 


must  not  be  dried,  but  is  used  in  the  fresh  moist  condition.  On  the 
large  scale  it  is  obtained  in  a  sufficiently  dry  condition  merely  by 
centrifuging. 

Para-nitroso-diethylaniline  is  obtained  in  a  similar  manner, 
except  that,  owing  to  the  very  great  solubility  of  the  hydrochloride, 
no  water  is  used  for  the  nitrosation  but  only  concentrated  hydro- 
chloric acid  and  saturated  sodium  nitrite  solution,  with  external 
cooling.  In  the  works  the  process  is  carried  out  in  enamelled  vessels, 
as  in  the  case  of  the  Tropaeoline  coupling. 


20  gms. 
Gallamide. 
500  gms. 
Alcohol. 
Nitroso- 
dimethyl- 
aniline  from 
75  gms. 
dimethyl- 
aniline. 


i  part 
Gallamine 
Blue. 
6  parts 

25% 
Bisulphite. 


(b)  Gallamine  Blue. 

20  Gms.  gallamide  of  92  %  purity  x  are  dissolved  in  500  c.cs.  of 
90  %  alcohol  contained  in  a  glass  bolthead  provided  with  reflux 
condenser  and  stirrer  (see  Figs.  9  and  i8A),  and  nitroso- dimethyl- 
aniline  obtained  from  75  gms.  dimethylaniline  are  added  in  three 
portions  to  the  boiling  mixture.  Preferably  the  additions  are  made 
at  intervals  of  15  minutes,  so  that  the  mixture  is  completed  in  three- 
quarters  of  an  hour.  The  product  is  boiled  up  under  reflux  for  a 
further  4  hours,  and  is  then  allowed  to  stand  for  12  hours.  The 
Gallamine  Blue  is  obtained  as  a  brilliant,  glistening,  bronzed  pre- 
cipitate which  is  filtered  off  and  washed  with  water.  The  alcohol 
is  redistilled.  The  yield  of  pure  Gallamine  Blue  is  about  40  gms. 
A  grey  dye  similar  to  Nigrosine  is  obtained  from  the  alcoholic  mother- 
liquor,  which  gives  fast  grey  shades  with  chrome  acetate  on  cotton 
under  the  name  of  Methylene  Grey. 

Gallamine  Blue  is  practically  insoluble  in  water  and  can  therefore 
not  be  used  in  this  form.  By  means  of  various  reactions,  however, 
it  may  be  converted  into  an  easily  soluble  form. 

One  part  Gallamine  Blue  is  warmed  up  to  50°  on  the  water-bath 
with  six  parts  of  sodium  bisulphite  solution  containing  25  %  SO2, 
until  the  evolution  of  sulphurous  acid  has  ceased.  If  this  is  the  case, 
after  about  an  hour  the  product  is  heated  up  to  85°  for  1-3  days  until 
the  colour  of  the  mixture  has  become  pure  greyish-green.  The  dye 
obtained  is  a  sulphonic  acid  of  the  leuco-compound  (or  possibly  a 
complex  sulphonic  salt),  and  dyes  wool,  mordanted  with  chrome 
acetate,  a  beautiful  and  fast  navy  blue.  It  may  also  be  used  for 
printing  cotton,  but  is  overshadowed  in  importance  by  another 
colouring  matter  belonging  to  this  group,  namely,  the  Modern  Violet 
of  Durand  and  Hugenin,  which  is  obtained  as  a  leuco-compound 

1  The  purity  is  determined  by  distilling  off  the  ammonia  with  caustic  soda 
solution  and  titrating. 


MISCELLANEOUS   DYES  173 

by  the  reduction  of  Gallamine  Blue  with  hydrogen  sulphide,  and 
affords  extremely  pure  and  fast  chrome  lakes  on  cotton  : 


HZ    CONH2 


Cl 


Modern  Violet  (Durand  and  Hugenin). 

50  Gms.  Gallamine  Blue  are  dissolved  in  about  40  gms."  of  30  %   50  gms. 
caustic  soda  solution  and  400  c.cs.  water,  and  to  the  clear  solution  ^^mm 
are  added  50  gms.  crystallized  sodium  sulphide.     The  liquid  is  40  gms. 
acidified  at  60°  during  one  hour  with  about  100  gms.  strong  hydro-   3°  % 
chloric  acid  until  a  permanent  reaction  is  given  with  Congo  paper.    .00  c  c's 
The  blue  colour  will  have  disappeared   by  this  time,  leaving   a  H2O. 
practically  colourless    solution,  which    is  filtered    from    the    pre-  jj 
cipitated  sulphur,  and  the  hydrochloride   of  the  leuco  compound  About 
salted  out  with   150  gms.  common  salt.     It  is   then  filtered  off,   I0°  g. 
washed  with  a   little  saturated  salt  solution,  and  well  pressed  out.   I50  gms 
The  dye  is  dried  in  vacuo  at  60°  as  it  rapidly  reoxidizes.     Yield  NaCl. 
about  55  gms. 

Notes  on  Works  Technique  and  Practice. — The  oxazines  are  print- 
ing colours  par  excellence.  In  addition  to  the  dimethylaniline 
derivatives  the  corresponding  diethyl  derivatives  are  also  prepared, 
which  are  characterized  by  their  very  pure  greenish  shades  (Celestine 
Blue).  If  gallic  acid  be  used  in  place  of  gallamide,  the  Gallocyanines 
are  produced  which  were  accidentally  discovered  by  Horace  Kochlin  ; 
he  attempted  to  fix  nitroso- dimethylaniline  on  cotton  by  means  of 
tannin  and  tartar  emetic,  and  so  obtained  blue  colours  which  he 
recognized  to  be  oxazines.  The  Gallocyanines  cannot  be  manu- 
factured conveniently  in  ethyl  alcoholic  solution,  methyl  alcohol 
being  used  instead,  which  is,  however,  less  pleasant  to  work  with 
owing  to  its  poisonous  nature  and  its  volatility.  Besides  the  simple 
oxazines  there  are  also  a  number  of  more  complex  condensation 
products  known,  but  we  cannot  enter  into  these  here. 

We  may  recall  the  fact  that  the  first  oxazine  to  attain  to  technical 

importance  was  Meldola's  Blue,  Naphthol  Blue,  or  Bengal  Blue, 

which  is  obtained  from  nitroso- dimethylaniline  hydrochloride  and 

•/3-naphthol.     It  is  very  fast,  but  does  not  give  beautiful  shades,  and 


174  DYES 

its  dust  attacks  the  mucous  membranes  so  strongly  that  many  people 
cannot  work  with  it.  In  spite  of  this,  however,  it  is  still  fairly  widely 
used. 

The  large-scale  plant  is  constructed  of  enamelled  cast-iron  with  a 
reflux  condenser  made  from  lead  tubing.  A  charge  of  40  kilos, 
gallamide  is  used,  the  operation  lasting  about  12  hours. 

Owing  to  its  oxidizability  Modern  Violet  must  be  ground  up 
in  the  cold  as  otherwise  spontaneous  combustion  may  occur.  The 
presence  of  finely  divided  sulphur  is  obviously  the  cause  of  this 
undesirable  phenomenon. 


Methylene  Blue  from  Dimethylaniline. 

The  formation  of  Methylene  Blue  is  of  interest  both  from  the 
scientific  and  technical  standpoints,  and  will  therefore  be  discussed 
before  the  actual  methods  of  preparation  are  described. 

Nitroso-dimethylaniline  is  prepared  from  dimethylaniline  by 
treating  the  latter  with  sodium  nitrite  in  hydrochloric  acid  solution. 
This  nitroso  compound  is  reduced,  giving  />-amino-dimethylaniline. 

Reactions  : 

(a)  />-Amino-dimethylaniline  : 


-NO  xx     xNH 


(CH3)2N/  (CH3)2N 

Dimethylaniline.  p-  Nitroso-dimethylaniline.        p-Amino-dimethylaniline . 

(b)  The  ^-amino-dimethylaniline  is  oxidized  in  acid  solution 
with  a  second  molecule  of  dimethylaniline,  and  at  the  same  time  the 
thiosulphonic  acid  group  is  introduced  into  the  molecule,  which  is 
effected  by  carrying  out  the  oxidation  in  the  presence  of  nascent 
thiosulphuric  acid.  . 

NKU  A   vNx-A 


(CH3)2N/\/\S  (CH3)2N/\/\S 


SO3H  SO3H 

Thiosulphonic  acid  of  p-amino-  Thiosulphonic  acid  of 

dimethylaniline.  Binds  chedler's  Green. 


MISCELLANEOUS   DYES  175 

(c)  The  thiosulphonic  acid  is  now  converted  into   Methylene 
Blue  .by  closing  the  ring  with  the  aid  of  more  oxidizing  agent : 


(a)  p-Amino-dimethylaniline. 

24*2  Gms,  (2/10  mol.)  of  pure  dimethylaniline  are  dissolved  in 
75  gms.  concentrated  hydrochloric  acid  (30  %)  and  is  then  allowed 
to  cool.  The  solution  is  treated  with  150  gms.  ice,  and  during  i  hour 
14*7  gms.  of  100  %  sodium  nitrite  are  run  in  as  a  20  %  solution, 
the  nitrosation  being  complete  in  4  hours.  A  further  no  gms.  of 
30  %  hydrochloric  acid  are  now  added,  together  with  200  gms.  ice, 
and  35  gms.  good  quality  zinc  dust  are  added  during  a  quarter  of  an 
hour  with  mechanical  stirring.  The  temperature  may  without  danger 
be  allowed  to  reach  25°.  The  solution  is  now  colourless  and  neutral 
to  Congo,  and  is  filtered,  the  zinc  dust  being  washed  out  with  a  very 
little  water. 

(b)  Thiosulphonic  Acid  of  Bindschedler's  Green. 

The  oxidation  at  this  stage  must  be  effected  in  the  presence  of  a 
zinc  chloride  solution  which  has  no  reducing  action.  Such  a  solution 
may  be  prepared  by  dissolving  sheet-zinc  in  concentrated  hydro- 
chloric acid.1  The  thiosulphuric  acid  is  used  in  the  form  of 
aluminium  thiosulphate,  which  is  so  strongly  dissociated  that  it 
behaves  like  free  thiosulphuric  acid. 

Before  beginning  the  actual  preparation  of  the  Methylene  Blue, 

1  A  method  adopted  in  the  works  is  to  treat  commercial  zinc  chloride  liquor 
with  sodium  bichromate  until  there  is  no  further  reducing  action  ;  frequently 
100-250  gms.  bichromate  are  required  for  100  kilos,  of  zinc  solution. 


24*2  gms. 
Dimethyl- 
aniline. 
75  gms. 
30  % 
HC1. 
150  gms. 
Ice. 

14-7  gms. 
ioo  % 
NaN02. 
no  gms. 
30% 
HC1. 


inc  dust. 


i76 


DYES 


4 

ioo  % 

H2S04. 

ioo  gms. 

50% 

ZnCl2. 

38  gms. 

A12(S04)3 

+  i8H2O. 

52-5  gms. 

Na2S2O3 

+SH20. 

19  gms. 

Na2Cr2O7. 

38  gms. 

Na2Cr2O7. 

25  gms. 

MnO, 

(about  88%). 


70  gms. 
H2SO4, 
66°  Be. 


i  litre  H2O. 


50  gms. 
ZnCl2, 
So  %. 
150  gms. 
NaCl. 


solutions  must  be  prepared  of  the  necessary  reagents,  as  an  essential 
point  in  this  operation  is  that  the  substances  shall  be  added  quickly 
and  at  the  right  temperature. 

Solution  I  =  38  gms.  pure  aluminium  sulphate  in  60  c.cs.  water. 

Solution  II  =  52*5  gms.  crystallized  sodium  thiosulphate  in 
50  c.cs.  water. 

Solution  III  =  57  gms.  sodium  bichromate  made  up  to  90  c.cs. 

Solution  IV  =  20  gms.  dimethylaniline  in  27  gms.  strong  hydro- 
chloric acid. 

"  Solution  "  V  —  25  gms.  very  finely  powdered  pyrolusite  (MnO2) 
made  up  into  a  homogeneous  paste  with  30  c.cs.  water. 

The  clear  neutral  solution  of  ^-amino-dimethylaniline  is  made 
mineral-acid  with  4  gms.  concentrated  sulphuric  acid  and  ioo  gms. 
of  50  %  non-reducing  zinc  chloride  solution  is  added.  The  beaker 
is  placed  on  a  felt  pad  and  heated  up  by  blowing  in  steam.  Solution  I 
is  added  at  the  ordinary  temperature  with  good  stirring,  then 
Solution  II,  and  after  2  seconds  one-third  of  Solution  II I, correspond- 
ing to  19  gms.  of  sodium  bichromate.  By  passing  in  dry  steam  the 
temperature  is  raised  to  40°  in  one  minute,  Solution  IV  is  added,  then 
the  remainder  of  Solution  III,  and  the  whole  heated  rapidly  to  70°. 
The  liquid  becomes  dark  greenish-blue,  owing  to  the  formation  of  the 
thiosulphonic  acid  of  Bindschedler's  Green.  As  soon  as  70°  is 
attained,  suspension  V  is  added,  and  the  whole  heated  to  85°. 

The  reason  for  adding  the  manganese  dioxide  is  to  convert  the 
sulphurous  acid  which  is  set  free  during  the  ring-formation  into  the 
harmless  dithionate.  In  place  of  the  pyrolusite,  40  gms.  copper 
sulphate  may  be  used  with  equal  success,  the  cupric  salt  being 
converted  into  the  insoluble  cuprous  salt. 

At  85°  the  solution  develops  a  fine  bronzed  appearance  and  the 
resultant  dye  is  precipitated  from  the  concentrated  zinc  chloride 
solution.  After  half  an  hour  the  mixture  is  allowed  to  cool  to  50°, 
and  70  gms.  concentrated  sulphuric  acid  are  added,  which  dissolves 
up  the  manganese  salt,  aluminium  hydroxide,  and  chromic  oxide. 
The  product  is  filtered  off  at  20°  and  washed  with  a  little  10  %  brine. 
The  crude  blue  is  dissolved  in  a  litre  of  water  at  100°,  filtered  from 
insoluble  matter,  and  the  clear  filtrate  salted  out  with  50  gms.  of 
ordinary  50  %  zinc  chloride  solution  and  150  gms.  common  salt. 
After  24  hours,  the  zinc  chloride  double  salt  comes  out  as  a  fine  red 
bronzed  precipitate  which  is  filtered  off  and  washed  with  a  little 
10  %  salt  solution  ;  it  is  then  dried  at  a  temperature  not  exceeding 
50°,  a  yield  being  obtained  of  about  44  gms.  pure  concentrated  colour. 


MISCELLANEOUS   DYES  177 

Notes  on  Works  Technique  and  Practice. — The  method  described 
above  was  originated  by  Bernthsen  and  Ulrich,  who  also  recom- 
mended the  use  of  aluminium  thiosulphate.  The  use  of  pyrolusite 
or  copper  sulphate  is  general.  Large  quantities  are  not  dealt  with 
at  one  time  as  quick  heating  up  is  essential.  On  the  large  scale  the 
finished  dye  is  usually  filtered  off  in  frame-filters  (see  Plate  VI.),  and 
after  draining,  is  put  into  small  bags  and  centrifuged. 

Owing  to  its  very  pure  shade  and  low  price,  Methylene  Blue  is 
Highly  valued,  and  is  much  used  for  dyeing  tannined  cotton.  For  silk 
printing  the  zinc-free  Methylene  Blue  is  used  for  the  production  of 
discharge  effects.  The  zinc-free  product  is  obtained  by  dissolving 
ordinary  Methylene  Blue  in  water,  precipitating  the  zinc  with  sodium 
carbonate,  and  filtering  off  the  solution  of  the  easily  soluble  Methylene 
Blue  base.  By  the  addition  of  hydrochloric  acid  and  common  salt, 
the  zinc-free  Methylene  Blue  is  precipitated  out  in  fine  crystals. 
On  the  large  scale  the  crystallization  occupies  several  days,  arid  is 
assisted  by  cooling  with  lead  pipes  through  which  cold  water  is 
circulated. 

Of  equal  importance  with  the  zinc-free  salt  of  Methylene  Blue 
is  the  nitro  compound  which  is  known  as  Methylene  Green.  The 
nitration  is  effected  in  a  similar  manner  to  that  of  Tropaeoline,  and 
the  crude  zinc  chloride  double  salt  may  be  nitrated  directly. 

The  crude,  moist,  Methylene  Blue  as  obtained  above  is  made  Crude  Blue 
into  a  paste  with  50  c.cs.  water  and  20  gms.  of  60  %  nitric  acid  (3/10  m°U. 
(40°  Be.),  and  to  it  is  added  at  25°,  5  gms.  sodium  nitrite  dissolved  in  H2of S 
the  minimum  quantity  of  water.     The  temperature  is  then  raised  20  gms. 
cautiously  to  50°  with  good  stirring  and  kept  there  for  2  hours.  f°3* 

The  product  is  diluted  up  with  200  gms.  of  saturated  brine,  and  the  NaNO3 
precipitate  filtered  off  after  12  hours.    The  crude  product  is  dissolved  -(approx. 
in  i  litre  of  water  at  a  temperature  not  higher  than  60°,  the  solution  200  gms. 
filtered  and  the  dye  precipitated  by  means  of  150  gms.  salt  and  50  gms.  NaCl  soln. 
of  50  %  zinc  chloride  solution.     After  standing  for  12  hours  the  I  lltre  Ha°- 
colour  is  filtered  off  and  dried  at  45°  until  it  can  be  powdered.     It  Nacf"1 
still  contains  about  20  %    of  water.      If  it  is  dried  completely  its  50  gms. 
strength  is  quickly  diminished,  a  portion  becoming  insoluble.     The  f 
yield  from   the   above  quantities   is   about  37  gms.   of  concentrated 
product. 

Methylene  Blue  and  Methylene  Green  are  brought  down  to 
standard  with  dextrine,  as  the  addition  of  salt  diminishes  the  solu- 
bility too  much.  The  most  important  use  for  Methylene  Green  is  in 
combination  with  iron-mordanted  logwood  for  dyeing  blacks  on 
silk,  but  it  is  also  much  used  in  conjunction  with  tin  phosphate. 

12 


178  DYES 

The    black    dyeings    obtained    in    this    manner    are    amongst  the 
finest  and  fastest  blacks  for  silk. 

If  diethylaniline  or  dimethyl-o-toluidine  are  used  in  place  of 
dimethylaniline,  the  pure  greenish  Thiazine  Blue,  also  known  as 
Thionine  Blue,  etc.,  is  obtained,  which  serves  for  the  production  of 
pure  blue  shades  on  silk  ;  its  importance,  however,  is  decreasing 
owing  to  the  competition  of  the  faster  Alizarin  colours.  The  non- 
alkylated  Methylene  Blue,  diamino-phenazthionium  chloride  or 
Lauth's  Violet,  is  used  to  a  very  limited  extent  for  pure  violet  shades. 
It  is  still  made  by  the  old  method,  which  consists  in  oxidizing  aniline, 
/>-phenylene  diamine,  and  hydrogen  sulphide  with  ferric  chloride. 


Safranine  from  o-Toluidine  and  Aniline.1 


_,..,     +  HCl+NaN02     f    V-NH-N2- 

*].        -» 


o-Toluidine. 


Aminoazo-o-toluene. 

CH, 


f^TJ 

3      4-0 

!NH2    ±B? 


CH9/V       m      ^n9      cl      ,    Aniline 


o-  Tolyl-indamine. 

The  methods  of  formation  of  the  Azines,  and  of  Safranine  in 
particular,  are  very  closely  connected  with  those  of  the  Thiazines 
(see  p.  174).  Of  the  numerous  methods  given  in  scientific  literature 
there  is  only  one  of  practical  importance,2  namely,  that  in  which 

1  For  more  exact  details,  see  J.  Walther,  "  Aus  der  Praxis  der  Anilinfarben- 
fabrikation,"  pp.  21  et  seq.  ;  291  et  seq. 

2  With  the  exception  of  the  Anthraquinone-azines,  and  certain  dyes  of  less 
importance. 


PLATE   XV. 


MISCELLANEOUS   DYES 


179 


(as  in  the  case  of  Methylene  Blue),  a  para-diamine  is  oxidized  with  a 
mono-amine  to  give  the  Indamine,  from  which  the  actual  azine  dye 
is  produced  by  the  closing  of  the  ring.  In  the  case  of  Methylene 
Blue  the  thiazine  ring  is  closed  with  a  sulphur  atom,  derived  from  the 
thiosulphonic  acid,  whilst  in  the  case  of  Safranine  this  position 
is  taken  up  by  an  aromatic  mono-amine,  usually  aniline.  The 
mechanism  of  the  reaction  is  indicated  in  the  above  scheme. 

Instead  of  isolating  the  pure  aminoazo- toluene,  the  resultant  azo 
compound  may  be  reduced  straight  away.  By  this  means  one 
molecule  of  ^-diamine  is  formed  together  with  two  molecules  of  a 
monoamine.1  Many  chemists  prefer,  however,  to  separate  out  the 
aminoazo-o-toluene  first,  which  is  then  reduced,  and  the  mixture  of 
^>-diamine  with  the  mono-amine  is  oxidized  to  the  Indamine. 

On  oxidizing  this  Indamine  together  with  hydrogen  sulphide,  for 
example  by  means  of  ferric  chloride,  the  homologue  of  Lauth's 
Violet  is  produced.  As  a  so-called  quinoid  Indamine  it  is  able  to 
condense  with  a  variety  of  substances.  With  aniline,  under  the 
oxidizing  influence  of  chromic  acid  or  recovered  manganese  sludge 
(see  p.  150),  a  condensation  product  is  first  formed  which  is  then 
oxidized  to  the  azine  by  the  further  action  of  the  oxidizing  agent  : 


+  0 


Cl 


Piimary  addition  product. 


o-Phenylamino-o-tolyl-indamine . 


o 


Cl 


Safranine. 


1  In  the  works,  for  practical  reasons,  enough  aniline  is  taken  to  give  equal 
molecules  of  aniline  and  o-toluidine. 


i8o 


DYES 


In  the  early  days  of  the  manufacture  of  Safranine,  an  excellent 
oxidizing  agent  was  made  use  of,  namely,  the  recovered  manganese 
dioxide  obtained  in  the  production  of  chlorine  by  Weldon's  method. 
Later,  as  the  Weldon  manganese  sludge  disappeared  from  the  market, 
use  was  made  of  chromic  acid  until  the  development  of  saccharine 
manufacture  again  placed  large  quantities  of  manganese  sludge  at 
the  disposal  of  the  dye  manufacturers.  It  appears,  however,  that 
the  Weldon  mud  cannot  be  altogether  replaced  by  the  manganese 
sludge  from  the  manufacture  of  saccharine,  so  that  at  the  present  time 
the  question  is  still  unsettled  as  to  the  most  advantageous  method. 
As,  however,  the  use  of  Safranine  has  also  meanwhile  diminished 
considerably,  the  question  has  now  largely  lost  its  importance  (see 
also  notes  on  Works  Practice). 


o-Toluidine, 
24  gms. 
Aniline. 
35  gms. 
30% 
HC1. 
22  gms. 
ioo  % 
NaNO2. 


1 80  gms. 
H20. 
1 80  gms. 
30% 
HC1. 

About ioo 
gms.  Fe. 


no  gms. 
CaC03. 


ioo  gms. 
Na2Cr2O, 
400  c.cs 
Ice-water. 


Mixture  of  Aminoazo-  Toluene  and  Aniline. 

54  Gms.  o-toluidine  (^  mol.)  are  mixed  with  24  gms.  aniline  and 
then  treated  with  35  gms.  of  30  %  HC1.  The  mixture  is  cooled 
externally  to  15°  and  diazotized  at  this  temperature  during  2  hours, 
with  continuous  stirring,  by  means  of  a  concentrated  solution  of 
22  gms.  ioo  %  sodium  nitrite,  after  which  the  mixture  is  warmed 
cautiously  during  i  hour  to  35°,  and  is  then  allowed  to  stand  for  at 
least  10  hours  at  30°.  60  C.cs.  water  are  then  added,  and  the  product 
run  off  from  the  salt  solution,  which  still  contains  a  little  nitrite. 

The  oily  mixture  of  aniline  and  aminoazo-toluene  is  now  treated 
with  1 80  gms.  of  30  %  hydrochloric  acid  and  the  same  quantity  of 
water,  ioo  gms.  iron  powder  being  then  sifted  in  ;  the  temperature 
should  remain  below  25°. 

The  product  is  kept  at  this  temperature  until  a  test-portion, 
extracted  with  a  little  ether,  no  longer  colours  the  latter  solvent. 
If  this  is  not  the  case  after  an  hour  a  little  extra  iron  is  added.  The 
fully  reduced  solution  is  now  filtered  and  made  up  to  600  c.cs.  This 
mixture,  containing  about  one  molecule  each  of  aniline,  o-toluidine, 
and  />-diamine  (mixture  of  phenylene-  and  toluylene-diamine)  is 
treated  with  no  gms.  finely  powdered  chalk,  and  as  soon  as  the 
evolution  of  carbon  dioxide  has  ceased,  the  volume  is  made  up  with 
water  and  ice  to  i  litre.  The  temperature  must  not  exceed  o°. 
The  mixture  is  now  treated  during  5  minutes  with  a  solution  of 
ioo  gms.  sodium  bichromate  in  400  c.cs.  ice- water  with  stirring,  which 
is  continued  for  a  further  12  hours.  It  is  a  good  thing  to  leave  the 
mixture  over-night,  after  which  it  is  boiled  vigorously  either  by 


MISCELLANEOUS   DYES  181 

blowing  in  steam  or  by  heating  in  a  porcelain  basin  for  half  an  hour. 

The  product  is  then  filtered  through  a  large  "  nutsch  "into  a  previously 

warmed  jar,  and  the  voluminous  residue  is  washed  out  with  half  a 

litre  of  boiling  water.     The  clear  filtrate  is  precipitated  by  means  of 

about  450  gms.  salt,  added  a  portion  at  a  time,  and  the  crude  Safranine 

is  filtered  off  after  cooling.     The  colour  is  still  rendered  impure  by 

the  presence  of  various  by-products,  which  must  be  removed.     For 

this  purpose  the  filter-cakes  are  dissolved  in  a  litre  of  boiling  water  About 

and  a  solution  of  2  gms.  sodium  bichromate  in  50  c.cs.  of  50  %  j^|  ^SQ   -m 

sulphuric  acid  is  added  cautiously  until  a  filtered  test-portion  appears  40  c.cs. 

as  pure  as  Safranine  (blue  shade).     The  whole  liquid  is  then  filtered,  f£  §Q 

treated  with  about  15  gms.  of  dehydrated  sodium  carbonate  (litmus  About 


should  just  be  turned  blue  by  the  liquid  after  salting  out),  and  the  35 
dye  precipitated  with  15  %  of  salt  ;  it  is  then  filtered  off,  pressed, 
and  dried.     Yield  of  dry  product  about  40  gms. 

The  product  may  be  further  purified  by  recrystallizing  from  water 
and  alcohol.  It  is  a  good  plan  to  stir  up  the  moist  press-cakes  with 
their  own  weight  of  alcohol  and  then  to  dissolve  up  by  boiling,  a  little 
water  being  added  if  necessary.  The  yield  of  crystallized  Safranine 
is  about  25  gms. 

Notes  on  Works  Technique  and  Practice.  —  The  importance  of 
Safranine  has  diminished  considerably  during  recent  years,  and  the 
price  has  fallen  to  such  an  extent  that  few  factories  concern  them- 
selves with  its  production.  The  reduction  is  also  carried  out  by 
means  of  tin  and  hydrochloric  acid,  the  tin  being  always  recovered  by 
means  of  zinc  dust.  With  the  old  process,  as  already  mentioned, 
the  oxidation  was  effected  with  recovered  manganese  dioxide  (in 
presence  of  oxalic  acid).  The  purification  of  the  dye  was  carried  out 
by  means  of  sodium  sulphate. 

The  chromic  oxide,  which  is  mixed  with  considerable  quantities 
of  iron  oxide,  cannot  be  converted  directly  into  chromic  salts  for 
tanning  purposes,  as  is  the  case  with  that  obtained  from  the  manu- 
facture of  anthraquinone  or  of  Acid  Violet.  It  is  therefore  necessary 
to  reconvert  the  dried  residues  from  the  filter-press  into  calcium- 
sodium  bichromate  by  treatment  with  saltpetre  and  sodium  car- 
bonate. This  process  is  carried  out  either  in  flat  cast-iron  roasting 
pans,  or,  better,  in  the  well-known  rotating  oxidizing  apparatus. 
(See,  for  example,  L.  Wickop,  "  Die  Herstellung  der  Alkali 
Bichromate.") 

The  Safranines  are  still  used  to  a  fair  extent  for  tannined  cotton, 
and  have  also  a  certain  importance  for  paper  staining  owing  to  their 
pure  shade  and  their  cheapness. 


i82  DYES 

More  yellowish  marks  are  made  from  mixtures  containing  more 
or  less  aniline.  If  ^-aminodimethylaniline  (see  Methylene  Blue) 
be  used  in  place  of  para-toluylene  diamine,  the  bluish  Clematines 
are  produced  which  were  formerly  utilized  in  considerable  quantities . 
As  the  Safranines  possess  at  least  one  free  amino  group,  they  may  be 
diazotized  and  coupled  with  various  phenols  and  amines.  In  this 
way  the  important  Indoines  are  formed  which  are  strong  basic  colours 
and  are  used  for  cotton  and  wool  under  various  designations  (Indoine, 
Janus  Black,  etc.). 


This  will  be  a  suitable  point  at  which  to  make  some  further 
general  remarks  upon  dyes,  as  in  the  case  of  the  Safranines  and 
related  dyes  especially,  the  conditions  connected  with  their  manu- 
facture have  altered  very  considerably  in  the  course  of  time.  It  has 
already  been  mentioned  that  the  choice  of  oxidizing  agents  for  the 
production  of  Safranine  has  been  dependent  upon  circumstances. 
The  most  suitable  oxidizing  agent  for  Safranine  disappeared  with 
the  gradual  diminution  of  Leblanc  soda  manufacture.  Such  more 
or  less  voluntary  changes  in  the  technology  of  the  artificial  organic 
colouring  matters  take  place  almost  continuously  before  our  eyes, 
and  it  is  therefore  very  important  for  a  colour  factory  always  to 
possess  some  unfailing  source  of  supply  for  any  given  product, 
and,  on  the  other  hand,  to  find  sufficient  outlet  for  all  by- 
products. 

I  will  give  a  few  typical  examples  in  order  that  the  would-be 
colour-chemist  may  gain  some  idea  of  the  importance  of  this  aspect 
of  the  problem.  In  the  short  descriptions  which  have  been  given 
in  this  book  we  have  become  acquainted  with  various  substances 
in  the  preparation  of  which  always  more  than  one  main  reaction 
product  is  formed.  In  this  connection  we  are  not  concerning 
ourselves  with  inorganic  by-products  such  as  sulphurous  acid, 
Glauber  salt,  or  thiosulphate,  but  only  with  those  organic  compounds 
which  it  is  customary  to  regard  as  the  actual  intermediates  for  the 
dye  industry. 

For  example,  in  the  manufacture  of  Cleve's  acids  and  of  the 
naphthylamine  sulphonic  acids  1:8  and  1:5  there  is  always  a  fairly 
constant  ratio  between  the  various  isomers,  which  all  have  to  be 
utilized.  Only  very  occasionally  is  one  forced  to  cast  part  of  the 
reaction  product  aside  until  some  satisfactory  and  profitable  method 
of  utilizing  it  is  evolved.  In  the  case  of  the  acids  mentioned  above 


MISCELLANEOUS  DYES  183 

the  position  is  very  simple,  as  in  the  event  of  stocks  of  one  of  them 
accumulating,  cheap  azo  dyes  are  produced  with  the  aid  of  /3-naphthol 
which  may  be  either  sold  as  such  or  in  Black  mixings. 

The  situation  is  not  so  simple  in  the  case  of  o-  and  ^-toluidine. 
When  Safranine  was  utilized  in  very  large  quantities  such  accumula- 
tions of  />-toluidine  were  obtained  that  the  discovery  of  dehydrothio- 
p-toluidme  came  quite  as  a  relief.  Then,  with  the  diminution  in  the 
demand  for  Safranine,  such  stocks  of  o-toluidine  collected  that 
cheap  p-iolmdme  could  only  be  obtained  from  the  aniline-oil 
factories  on  condition  that  a  certain  quantity  of  o-toluidine  was  also 
taken,  the  price  of  which  sometimes  sank  below  50  centimes.  In  a 
similar  way  the  price  of  m-toluidine  also  fell  below  i  franc  per  kilo., 
owing  to  the  absence  of  demand.  Then  again,  for  a  certain  period, 
the  toluidine  question  lost  its  importance  as  trinitrotoluene  could  be 
made  from  the  o-nitrotoluene,  which  was  used  in  large  quantities 
as  a  shell-filling. 

Another  similar  case  is  that  of  o-  and  ^-nitrochlorbenzene  ;  for 
a  long  time  the  demand  for  />-nitrochlorbenzene  was  far  in  excess  of 
that  for  the  ortho  compound.  Then  Sulphur  Black  T  required  such 
quantities  of  dinitrochlorbenzene  that  all  the  mononitro  product  was 
readily  absorbed.  The  increasing  competition  in  Sulphur  Black  T 
made  the  problem  again  acute,  and  large  quantities  of  ortho-nitro- 
chlorbenzene  were  amassed  until  the  production  of  o-nitroanisole — 


J^Q        n^v^i*3w.LT.«  -r-w  }         jxT/^  Nad 


— for  the  preparation  of  o-dianisidine  caused  so  great  a  demand  for 
the  ortho  product  that  it  became  difficult  to  find  sufficient  use 
for  the  para  product.  Possibly  the  method  for  the  preparation 
of  ^>-nitraniline  given  on  p.  72  may  offer  a  way  out  of  the 
dilemma. 

Analogous  cases  are  the  simultaneous  production  of  R-salt  and 
G-salt,  the  formation  of  ortho-  and  />-nitrophenol,  and  so  on.  In 
many  cases  it  is  possible  by  suitable  alterations  in  the  method  of 
manufacture  to  suppress  one  product  (compare  for  example  the  two 
methods  for  the  preparation  of  amido-G-salt  given  on  pp.  35  and 

36). 

Again,  aminonaphthol  sulphonic  acid  1:8:4,  f°r  instance,  may  be 
obtained  via  the  naphthylamine  sulphonic  acid  1:8  (p.  30,  III),  or 
directly  from  naphthalene  by  disulphonation  and  nitration. 


184 


DYES 


Reaction  : 


S03H 


SO.H 


NO9  SOQH 


2  OW3J 


H03S 


le  -* 


S09H 


H03S      N02 

(=1:4:8). 


NH2  S03H  H03S      OH 


HOgS 


vX      \ 

e-acid. 


S03H 

3-0CM*. 

A  certain  quantity  of  the  /3-nitro  acid  is  formed  at  the  same  time 
which  yields  naphthylamine  disidphonic  acid  2:4:8  on  reduction. 

Other  substances  also  may  in  time  accumulate  in  such  quantities 
that  it  becomes  essential  at  last  to  make  use  of  the  ever-increasing 
waste- dumps,  as  only  rarely  is  it  decided  to  get  rid  of  by-products 
simply  by  burning  them.  An  interesting  case  of  this  is  the  neat 
method  worked  out  by  C.  Mettler  for  utilizing  the  o-chlorbenzoic 
acid  which  is  obtained  in  considerable  quantities  as  a  by-product  in 
the  manufacture  of  o-chlorbenzaldehyde.  The  resinous  masses  of 
crude  o-chlorbenzoic  acid  finally  attained  the  dimensions  of  a  small 
hill,  so  that  it  was  estimated  that  about  30,000  kilos,  of  pure  o-chlor- 
benzoic acid  remained  unused  for  years.  Attempts  to  convert  the 
acid  into  anthranilic  acid  by  treatment  with  ammonia  and  a  little 
copper,  or  a  cupric  salt,  by  Ullmann's  method,  showed  that  the  well- 
known  B.A.S.F.  method  (from  phthalic  acid  via  phthalamide  and 
oxidation  with  the  exactly  calculated  quantity  of  sodium  hypochlorite 


MISCELLANEOUS   DYES 

by  A.  W.  Hoffmann's  method)  gave  a  much  cheaper  and  purer 
anthranilic  acid. 

C.  Mettler's  device  consisted  in  obtaining  the  hitherto  unknown 
azo-salicylic  acid  by  a  roundabout  way  from  o-chlorbenzoic  acid, 
as  it  was  certain  from  L.  Oswald's  experiments  that  this  substance 
would  possess  remarkable  dyeing  properties.  This  interesting 
process  is  effected  in  the  following  way  :  nitrochlorbenzoic  acid  is 
obtained  by  the  nitration  of  the  o-chlorbenzoic  acid  ;  this  is  reduced 
with  zinc  dust  in  neutral  solution  to  aminochlorbenzoic  acid  which  is 
diazotized  and  coupled  with  salicylic  acid  and  the  chlorine  of  the 
valueless  azo  dye  replaced  by  heating  to  135°  with  caustic  soda  lye 
and  a  little  copper  oxide.  In  this  manner  azo-salicylic  acid  is 
obtained,  the  chrome  lake  of  which  is  distinguished  by  its  remarkable 
strength  and  great  fastness  towards  light,  milling  and  potting  ;  it 
also  levels  admirably  and  has  therefore  become  a  very  welcome 
addition  to  the  pattern-card.  The  following  formulae  will  illustrate 
the  reactions  involved  : 


HOOC 


HOOC 


+HNCX 


NO, 


NH2 

diazotized  and 
coupled  with 
salicylic  acid. 


o-Chlorbenzoic  acid, 


Nitrochlorbenzoic  acid. 


Aminochlorbenzoic  acid. 


-No- 


COOH  HOOC 

20%NaOH 
Cl 


Valueless  azo  dye. 


_N2-/    \COOH 

\JOH 

Azo-salicylic  acid  =  Erio  Chrome  Flavine  A. 


It  is  not  possible  to  obtain  this  compound  by  coupling  amino- 
salicylic  acid  with  salicylic  acid,  as  this  combination  can  only  be 
effected  directly  to  a  very  small  extent  (L.  Oswald,  v.s.). 

These  few,  though  characteristic  examples,  will  suffice  to  show 
that  with  many  dyes  new  problems  will  constantly  occur  according  to 
the  demand,  which  may  in  some  cases  take  years  to  solve. 


1 86  DYES 

10.    SUMMARY    OF    THE    MOST    IMPORTANT    METHODS 
USED  IN   THE   PREPARATION   OF  SYNTHETIC  DYES 

Sulphonations, 

1 .  An  aromatic  substance  is  treated  with  concentrated  sulphuric 
acid. 

2.  An  aromatic  substance  is  treated  with  sulphuric  acid  containing 
sulphur  trioxide  (Oleum). 

3.  By  heating  the  acid  sulphate  of  an  amino  compound  to  a 
moderately  elevated  temperature  (Bake  process). 

4.  Sulphonation  with  chlorsulphonic  acid. 

5.  By  converting  a  nitroso  compound  into  the  hydroxylamine 
sulphonic  acid,  and  this  in  its  turn  into  the  amino-hydroxy  sulphonic 
acid. 

6.  Replacing  an  easily  removable  chlorine  atom  in  an  aromatic 
substance  by  a  sulphonic  group,  by  heating  with  a  sulphite. 

Nitrations, 
i*  Direct  nitration  by  means  of  concentrated  nitric  acid. 

2.  The  substance  to  be  nitrated  is  first  sulphonated  and  the 
sulphonic  group  is  then  replaced  by  NO2  by  the  vigorous  action  of 
nitric  acid,  frequently  with  the  assistance  of  sulphuric  acid. 

3.  By  nitrosating  an  amine,  oxidizing  with  dilute  sulphuric  acid, 
to  the  nitramine,  which  is  then  transformed  to  the  nitro  compound. 

4.  By  heating  a  diazonium  nitrate  with  dilute  nitric  acid. 

Reductions. 

1.  Reduction  with  iron  and  water,  in  presence  of  much,  little,  or 
no  acid,  or  in  presence  of  caustic  soda  lye. 

2.  Reduction  with  hydrogen  sulphide  or  with  its  neutral  and 
acid  salts. 

3.  Reduction  by  means  of  sulphurous  acid. 

4.  Reduction  by  means  of  zinc,  zinc  dust,  or  tin. 

5.  Reduction  by  means  of  nascent  electrolytic  hydrogen. 

6.  Reduction  with  ferrous  hydroxide  (very  occasionally). 

7.  Reduction  by  means  of  hydrosulphite  (anthraquinone  series). 

Oxidations. 

1.  Oxidation  with  atmospheric  oxygen. 

2.  Oxidation  with  chromic  acid. 

3.  Oxidation  with  MnO2  or  manganese  mud  (Mn3O4). 


MISCELLANEOUS  DYES  187 

4.  Oxidation  with  sodium  hypochlorite  in  alkaline  solution. 

5.  Oxidation  with  nitric  and  nitrous  acids. 

6.  Indirect  oxidation,  by  chlorinating  and  subsequent  treatment 
of  the  chloride  with  water. 

7.  Oxidation  with  lead  peroxide  (PbO2). 

8.  Oxidation    by    means    of   nitrosyl    sulphuric    acid    (Aurine, 
Sandmeyer). 

9.  Oxidation  with  ferric  chloride  (Helvetia  Blue,  formation  of 
sulphones  from  sulphinic  acids  and  />-diamines). 

10.  Oxidation  with  bichromate  plus  a  ferrous  salt  (Safranine, 
Methylene  Blue,  etc.). 

1 1 .  Oxidation  in  presence  of  an  excess  of  one  of  the  components 
used  for  a  condensation  (nitroso  dimethylaniline  in  the  preparation 
of  Oxazines,  for  example). 

Alkali  Fusions. 

1.  Open  melt  with  caustic  soda,  caustic  potash,  or  mixture  of 
the  two. 

2.  Fusion  with  sodamide  alone,  or  mixed  with  caustic  soda  and 
caustic  potash  (Indigo). 

3.  By  heating  with  aqueous  alkali  under  pressure. 

4.  Melting  with  alkali  with  the  addition  of  an  oxidizing  agent 
(Alizarin,  Indanthrene). 

5.  Fusion  with  lime  (which  in  the  anthraquinone  series  prevents 
the  entrance  of  further  hydroxyl  groups). 

Methods  of  Coupling. 

1 .  Coupling  is  effected  in  the  presence  of  sodium  carbonate. 

2.  Coupling  is  effected  in  the  presence  of  caustic  soda. 

3.  Coupling  is  effected  in  the  presence  of  sodium  carbojiate, 
caustic  soda,  or  ammonia  being  added  subsequently. 

4.  Coupling  is  effected  in  the  presence  of  lime  or  magnesia, 
especially  in  the  case  of  nitroamino  compounds  (Sandmeyer). 

5.  Coupling  is  effected  in  the  presence  of  sodium  acetate,  to 
combine  with  the  acid  (the  acetate  may  usually  be  replaced  by  the 
formate,  but  this  requires  subsequent  neutralization). 

6.  Coupling  is  effected  in  the  presence  of  mineral  acid,  either 
without  neutralization,  or  the  mineral  acid  is  neutralized  cautiously 
by  means  of  sodium  carbonate  or  acetate. 

7.  Very  easily  oxidizable  substances  may  be  coupled  under  a 
layer  of  petroleum  (e.g.  i:5-dihydroxynaphthalene). 


III.  TECHNICAL   DETAILS 

//.     VACUUM     DISTILLATIONS     IN     THE     LABORATORY 
AND  IN   THE    WORKS 

THE  process  of  distilling  under  reduced  pressure,  commonly  called 
Vacuum  Distillation,  is  one  of  the  most  important  operations  in 
colour  technology.  Certain  products  are  distilled  under  reduced 
pressure  because  they  decompose  at  their  boiling  point  under 
ordinary  atmospheric  pressure,  and  also  because  vacuum  distillation 
offers  certain  other  advantages.  Owing  to  the  lower  boiling  point, 
the  radiation  losses  are  smaller  and,  in  addition,  it  is  often  possible 
to  heat  with  steam  instead  of  with  fire,  so  that  the  apparatus  may 
be  placed  wherever  it  is  most  convenient  without  any  danger  of 
fires.  In  addition,  there  is  another  very  important  circumstance 
which  by  itself  often  makes  it  desirable  to  distil  various  substances 
under  reduced  pressure,  namely,  the  easier  separation  of  mixtures 
composed  of  substances  whose  boiling  points  lie  close  together. 
Thus  it  is  only  possible  to  effect  a  satisfactory  separation  of  the  three 
isomeric  nitro-toluenes  by  distillation  in  vacuo,  and  the  alkyl-benzyl- 
anilines  also  can  only  be  separated  easily  into  their  components  in 
vacuo. 

Whilst  the  fractionating  columns  used  in  the  laboratory  are  for 
the  most  part  of  older  and  well-known  forms,  on  the  technical  scale 
new  and  complicated  pieces  of  apparatus  have  gradually  been  evolved. 
The  older  types  of  columns,  in  which  the  rising  vapours  had  to  pass 
through  a  downward  stream  of  liquid  by  means  of  which  they  were 
washed  or  dephlegmated,  are  becoming  obsolete,  and  are  rapidly  being 
replaced  by  more  modern  and  efficient  columns. 

The  principal  of  these  new  columns  is  as  follows  :  The  vapours 
must  take  as  long  a  path  as  possible  through  the  downward  stream  of 
liquid,  but  must  meet  with  only  slight  resistance.  Further,  the 
stream  of  liquid  must  be  finely  divided,  so  as  to  offer  as  large  a  surface 
as  possible  for  the  interchange  of  the  various  high-boiling  substances. 
At  the  present  day  there  are  two  important  types  :  First,  the 
Kubierschky  column,  in  which  the  gases  have  to  take  a  zig-zag  course, 

1 88 


. 


PLATE   XVI 


3  8.2 


rt 


>> 

.n 


VACUUM   DISTILLATIONS  189 

during  which  they  meet  with  a  descending  shower  of  liquid.  Plate  IX 
shows,  in  section,  two  forms  of  this  extremely  efficient  apparatus. 
They  are  used  not  only  for  fractional  distillation,  but  also  for  the 
removal  of  ammonia  from  gas-liquor,  for  obtaining  bromine  from 
Stassfurth  mother-liquors,  and  for  many  other  purposes.  If  it  is 
used  for  distillation  the  upper  opening  is  closed,  the  top  portion  of 
the  column  being  cooled  by  spraying,  whilst  the  remainder  (9/10- 
19/20)  is  insulated. 

The  other  form  of  construction,  due  to  F.  Raschig,  consists  in  a 
tower  filled  with  small  cylinders,  of  equal  height  and  diameter.  On 
filling  a  tower  with  such  cylinders  they  lie  irregularly,  as  indicated 
in  the  drawing  on  Plate  IX,  so  that  the  surface  with  which  the  gas 
and  liquid  come  in  contact  is  very  considerable. 

The  vacuum  is  produced  by  means  of  a  reciprocating  pump,  which 
brings  down  the  pressure  to  about  50  mms.  of  mercury.  Lower 
pressures  down  to  about  8  mms.  may  be  obtained  by  running  two 
pumps  in  series.  But  here  also  there  has  been  a  change  during  the 
last  few  years  ;  of  late  increasing  use  is  being  made  of  modern 
rotating  pumps,  such  as  the  excellent  pumps  made  by  the  Swiss 
Locomotive  and  Machine  Factory  in  Winterthur,  diagrams  of  whose 
compression  and  vacuum  pumps  (Witte's  system)  are  shown  on 
Plate  XVI.  The  method  of  working  is  indicated  by  the  diagram- 
matic sketch  :  the  movable  slides  enclose  a  definite  volume  of  air 
and  drive  it  towards  the  exit-opening,  by  which  means  it  is  com- 
pressed. The  machine  is  reversible,  and  may  be  used  either  as  a 
compressor  or  as  a  vacuum  pump,  pressures  being  obtainable  with 
it  from  about  4  atmos.  down  to  about  12  mms.  The  machine 
must  be  cooled,  as  may  be  seen  from  the  drawing.  It  is  coupled  up 
directly  with  an  A.C.  motor,  giving  1500-2500  revolutions  per 
minute,  the  loss  of  power  on  the  transmission  being  almost  negligible. 
As  already  mentioned,  two  rotating  pumps  are  frequently  coupled  up 
together,  one  behind  the  other. 

Where  it  is  desired  to  subject  liquids  to  a  vacuum  distillation, 
an  ordinary  boiler  is  made  use  of,  which  is  frequently  of  very  large 
capacity.  For  instance,  as  much  as  20,000  kilos,  of  aniline  may  be 
vacuum  distilled  in  a  boiler  which  is  heated  by  means  of  several  steam 
coils.  The  case,  however,  is  different  when  dealing  with  /5-naphthol 
or  a  similar  product,  and  such  large  quantities  cannot  be  distilled 
at  once.  Quantities  of  2000  kilos,  and  over  can  indeed  be  dealt  with, 
but  a  different  type  of  apparatus  is  required.  The  high  boiling 
point  of  /3-naphthol  prevents  steam  being  used  for  heating,  although 
here  also  very  promising  experiments  have  been  made  with  the 


190  TECHNICAL  DETAILS 

Frederking  apparatus.  Normally  the  heating  must  be  done  by  direct 
firing,  and  for  this  purpose  gas  heating  is  the  most  satisfactory,  owing 
to  the  ease  with  which  it  can  be  regulated.  Very  often  the  use  of  an 
oil-bath  is  omitted,  but  in  this  case  there  is  the  risk  of  the  residual 
pitch  becoming  charred,  so  that  it  is  difficult  to  remove  it  from  the 
still,  and  it  ceases  to  be  of  commercial  value.1  On  the  large  scale 
it  is  unnecessary  to  introduce  air  during  a  vacuum  distillation,  as 
"  bumping  "  does  not  occur.  It  is,  however,  necessary  for  the  whole 
apparatus  to  be  well  insulated,  and  also  that  all  tubes  in  which  stop- 
pages might  occur  shall  be  easily  accessible  and  capable  of  being 
heated  ;  the  receiver  must  be  provided  with  a  jacket  both  for  heating 
and  cooling.  After  the  distillation  is  finished  the  residual  liquid 
is  blown  out  of  the  still  through  a  tube  into  closed-in  moulds  to  avoid 
the  inconvenience  of  any  escaping  vapours.  A  large  empty  boiler 
is  placed  between  the  pump  and  the  receiver,  in  order  to  catch  the 
water  and  any  sublimate  which  may  be  formed.  Particularly  in 
the  case  of  |3-naphthol,  large  quantities  of  the  product  are  carried 
over  as  a  fine  snow  which  would  stop  up  the  pump. 

With  such  large  apparatus  several  thermometers  are  required  ; 
one  goes  to  the  bottom  of  the  still,  thus  permitting  the  temperature 
of  the  crude  mixture  to  be  ascertained,  so  that  it  is  possible  to 
recognize  when  the  distillation  is  just  beginning  and  when  it  is  coming 
to  an  end.  When  the  difference  in  temperature  between  the  vapours 
which  are  distilling  over  and  the  residue  in  the  still  exceeds  50°,  the 
process  should  be  stopped,  or  else  the  pitch  will  be  charred. 

The  illustration  on  Plate  X  shows  an  installation  for  the  distilla- 
tion of  /2-naphthol  ;  it  is  heated  by  means  of  three  gas-rings,  and  is 
calculated  for  a  charge  of  1000  kilos.  ;  such  a  distillation  should 
occupy  about  4  hours.  The  pitch  constitutes  about  5  %  of  the 
crude  naphthol.  The  naphthol  is  allowed  to  solidify  in  moulds 
like  sugar-loaves,  and  after  disintegration  it  is  "  whizzed." 

For  liquids,  worm-condensers  may  be  used,  or  straight  tubular 
condensers  containing  from  20-30  tubes.  Condensers  of  this  type 
may  also  be  heated  in  order  that  diphenylamine  or  other  easily  fusible 
substances  may  be  used  with  them  if  it  is  preferred  not  to  distil  them 
with  steam  (see  p.  99). 

Frequently  also  an  observation  window  is  placed  in  the  vertical 
portion  of  the  condenser,  through  which  the  stream  of  liquid  may  be 
accurately  observed. 

1  Naphthol  pitch  is  an  important  commercial  product.  It  is  a  black,  brittle 
mass  with  a  vitreous  lustre,  which  is  used  as  an  insulating  material  for  covering 
the  joints  of  electric  cables. 


VACUUM   DISTILLATIONS 


i9r 


192  TECHNICAL   DETAILS 

For  laboratory  use  the  arrangement  shown  in  Fig.  27  works  very 
well.  The  distilling  flask  possesses  a  double  neck,  one  for  the  fine 
capillary  and  one  for  the  thermometer,  and  at  the  same  time  this 
arrangement  prevents  the  contents  from  spurting  over.  Heating 
should  never  be  done  directly,  but  always  by  means  of  an  oil-bath, 
the  temperature  of  which  is  30-40°  higher  than  the  distilling  tempera- 
ture. The  capillary  is  drawn  out  from  an  ordinary  thin  glass  tube, 
and  should  be  soft  and  flexible  like  a  silk  thread  ;  it  should  just 
touch  the  bottom  of  the  flask,  and  the  upper  part  should  be  closed 
with  a  piece  of  pressure  tubing  and  a  screw  pinch-cock.  Just  enough 
air  should  be  allowed  into  the  flask  during  the  distillation  to  keep 
it  going  quietly. 

An  ordinary  distilling  flask  with  a  long  neck  is  used  as  a  receiver, 
and  not  any  complex  piece  of  apparatus.  If  several  different  frac- 
tions are  to  be  obtained,  the  distillation  is  stopped  for  a  moment 
and  the  receiver  changed,  which  occupies  only  a  few  seconds.  The 
method  of  cooling  may  be  seen  from  the  sketch.  The  manometer 
is  not  placed  in  the  pump  circuit,  but  is  attached  to  a  separate  tube 
in  order  to  prevent  any  liquid  from  getting  into  it.  The  safety  tap 
shown  is  of  some  importance,  as  it  permits  the  introduction  of  a  little 
air  if  the  liquid  in  the  distilling  flask  begins  to  show  signs  of  frothing 
over  ;  by  this  means  any  distillation  may  be  carried  out  in  a  short 
time.  The  pump  should  be  separated  from  the  distilling  apparatus 
by  means  of  a  large  safety  bottle.  It  is  advisable  that  the  water-pump 
be  connected  to  the  main  supply  pipe,  in  order  to  be  independent  of 
variations  in  pressure. 

Method  of  carrying  out  the  distillation. — The  oil-bath  is  heated  up 
to  the  correct  temperature  and  the  pump  started.  Usually  a  little 
water  or  solvent  comes  over  first,  so  that  the  vacuum  must  be  reduced 
by  means  of  a  safety  tap.  After  a  time  the  product  becomes  quietly 
fluid,  and  the  capillary  is  regulated  so  as  to  allow  a  vigorous  stream  of 
very  small  air-bubbles  to  pass  through.  After  a  time  the  distillation 
begins,  which  offers  no  difficulties  in  the  case  of  liquids,  but  the  side 
tube  tends  to  become  stopped  up  in  the  case  of  solid  products,  such 
as  yS-naphthol,  naphthylamine,  etc.  '  For  this  reason  the  neck  of  the 
flask  is  heated  up  before  the  beginning  of  the  distillation,  so  that  the 
first  drops  may  be  superheated.  Sometimes  it  may  even  be 
necessary  to  heat  up  the  portions  where  the  corks  are  by  means  of  a 
Bunsen  flame,  in  order  to  force  the  distillate  to  pass  over.  With  good 
quality  resistance  glass  there  is  no  danger  of  cracking,  but  at  the  same 
time  it  is  always  advisable  to  wear  a  pair  of  safety  goggles.  The 
distillation  should  always  be  carried  out  quickly  ;  for  example, 


CONSTRUCTION  AND   USE  OF  AUTOCLAVES    193 

200  gms.  /3-naphthol  can  be  distilled  in  15-20  minutes,  the  receiver 
being  kept  moderately  cool.  The  manometer  is  isolated  from  the 
rest  of  the  apparatus,  and  is  only  connected  up  from  time  to  time  to 
test  the  vacuum.  Beginners  often  daub  their  apparatus  with 
paraffin,  collodion,  and  other  substances,  in  order  to  make  them  air- 
tight, but  this  is  quite  unnecessary.  The  simplest  method  is  to  take 
good  quality  corks  and  to  soak  them  well  in  hot,  hard  paraffin-wax 
beforehand,  which  renders  any  further  treatment  unnecessary.  It 
is  only  necessary  to  use  rubber  stoppers  when  working  with  a  very 
high  vacuum,  though  for  this  purpose  an  apparatus  that  has  been 
blown  together  is  still  better. 

The  distilled  substance  is  melted  by  heating  over  a  bare  flame, 
and  the  liquid  is  poured  into  a  small  porcelain  dish.  The  solidified 
product  is  pure  and  should  not  be  further  recrystallized. 


12.   NOTES  UPON   TUB   CONSTRUCTION  AND   USB  OF 
AUTOCLAVES. 

Autoclaves  or  pressure  vessels  are  always  used  in  cases  where  it 
is  necessary  to  raise  the  temperature  of  a  substance  above  its  boiling 
point,  or  where  gases  are  evolved  on  heating,  which  are  necessary  for 
the  reaction.  In  this  connection  the  most  important  substances 
dealt  with  in  colour  technology  are  aqueous  solutions  and  mixtures, 
and  after  that  alcohol  and  alkyl  chlorides.  The  limits  of  pressure 
and  temperature  are  about  60  atmos.  and  300°  C.  Generally  speaking 
the  ordinary  type  of  apparatus  is  not  calculated  to  withstand  greater 
stresses  than  those  indicated. 

Both  vertical  and  horizontal  autoclaves  are  made  use  of,  either 
with  or  without  stirring-gear.  If  the  mixture  is  homogeneous, 
stirring  is  unnecessary  ;  but  if  several  layers  are  formed,  or  it  is 
necessary  to  bring  together  solid  and  liquid  substances,  then  con- 
tinuous stirring  is  essential.  As  an  example  of  a  reaction  carried  out 
under  pressure  in  which  stirring  is  unnecessary,  the  ordinary  prepara- 
tion of  dimethylaniline  may  be  given  ;  whilst  all  alkali-fusions  afford 
examples  where  continuous  stirring  is  requisite. 

The  autoclaves  used  are  hollow,  cylindrical  vessels  of  100-10,000 
litres  capacity,  provided  with  a  flange  to  which  the  cover  is  affixed 
by  means  of  nuts  and  bolts  ;  for  the  sake  of  greater  strength,  the 
bottom  is  usually  made  hemispherical.  They  are  almost  invariably 
made  of  iron,  either  cast  iron  or  cast  steel  being  used,  the  latter 
offering  the  greater  measure  of  safety  for  working  at  high  pressures 


194  TECHNICAL   DETAILS 

(see  also  steel  and  iron  as  structural  materials).  Besides  cast  iron 
and  steel,  tin  is  also  used  ;  autoclaves  made  of  tin  are  manufactured, 
having  walls  up  to  40  mms.  thick  ;  they  are  either  riveted  or  auto- 
genously  welded.  The  objection  taken  to  welded  autoclaves  by 
many  colour  factories  is  quite  unjustified,  and  is  explained  simply 
by  the  fact  that  at  first  the  welding  process  had  not  been  fully 
perfected. 

The  screw-bolts  form  the  weak  point  in  every  autoclave,  and  they 
must  therefore  be  made  from  the  best  hand-forged  wrought  iron. 
The  cover  has  flange-pieces  cast  on,  as  indicated  in  Fig.  32.  These 
serve  for  affixing  the  armatures  and  the  stuffing-box  of  the  agitator. 
The  bracket  which  bears  the  agitator  should  be  high  enough  to  make 
it  easy  for  the  packing  of  the  stuffing-box  to  be  looked  after  and 
renewed.  The  stuffing-box  itself,  through  which  the  axle  of  the 
stirrer  goes,  should  be  as  simple  as  possible,  and  cooled  with  water. 
Hollow  stuffing-boxes  are  also  cast,  through  which  water  may  be 
circulated.  Cooling  by  means  of  circulating  oil,  such  as  is  done  with 
success  in  the  case  of  steam  turbines  is  here  unnecessary,  as  the 
conditions  are  quite  different.  The  cover  is  provided  with  two 
manometers  and  two  thermometers,  together  with  two  safety  valves. 
Of  recent  years  it  has  become  the  custom  in  certain  cases,  with  the 
approval  of  experts,  to  do  away  with  the  safety  valves,  as  these  never 
work  properly  and  are  a  constant  source  of  annoyance.  By  using  two 
thermometers  and  manometers  it  is  easily  possible  to  follow  the 
course  of  a  reaction  exactly.  With  large  autoclaves  the  cover  is 
provided  with  a  special  opening  or  man-hole,  this  alone  being  opened 
from  time  to  time  as  occasion  requires.  The  joint  between  the 
cover  and  the  body  of  the  vessel  is  made  tight  by  means  of  a  special 
packing  ring  let  into  the  flange  of  the  autoclave  itself,  suitable 
materials  for  the  ring  being  copper,  lead,  lead-covered  iron,  or 
asbestos  board.  The  rings  must  be  accurately  turned,  and  must 
have  a  width  of  20—50  mms.  and  a  thickness  of  i— 6  mms.  Lead  is 
somewhat  easily  squeezed  out  by  the  pressure  of  the  screws,  but 
withstands  ammonia  very  well  ;  copper  is  the  ideal  packing,  but  is 
attacked  by  ammonia.  Asbestos  can  be  used  for  low  pressures,  but 
has  the  disadvantage  that  it  nearly  always  tears  when  the  autoclave 
is  opened.  The  cover  is  screwed  on  by  first  tightening  lightly 
diametrically  opposite  bolts,  and  then  working  round  in  a  circle, 
always  screwing  up  tighter  and  tighter,  the  final  tightening  being 
effected  by  hammering  the  long  wrenches  employed  for  the  purpose  ; 
there  is  no  danger  of  the  bolts  being  broken  off  in  the  process. 

The  walls  of  an  autoclave  should  never  be  brought  into  contact 


CONSTRUCTION  AND   USE   OF  AUTOCLAVES     195 

directly  with  the  substances  under  reaction,  as  every  melt  attacks  the 
walls,  so  that  after  a  time  the  apparatus  becomes  too  weak  and  must 
be  taken  down.  For  this  reason  a  lining  is  nearly  always  inserted 
in  the  actual  pressure- vessel,  and  is  kept  in  position  by  pouring  in 
solder.  It  is  not  permissible  simply  to  place  the  liner  in  the  autoclave 
as  the  heat  transmission  is  inadequate  and  the  walls  of  the  autoclave 
may  become  red-hot.  When  placing  the  liner  in  position  the  latter 
is  fixed  immovably  in  the  autoclave  by  means  of  a  strong  girder,  and 
then  the  solder  is  poured  in  through  a  sheet-iron  funnel.  Enamel 
and  lead  may  be  protected  by  covering  the  inside  of  the  liner  with  wet 
cloths,  or  it  may  be  filled  with  water  which  must,  however,  be  heated 
up  and  afterwards  cooled  by  means  of  a  worm.  If  the  heating  be 
omitted  it  is  quite  possible  for  the  solder  never  to  reach  the  bottom, 
but  to  solidify  half-way  down  ;  if,  on  the  other  hand,  the  inner  vessel 
be  cooled  by  water  without  using  a  coil,  then  the  water  will  boil  away 
altogether. '  An  inadequate  heat  transmission  may  be  caused,  how- 
ever, not  only  by  the  presence  of  air  in  the  intervening  space,  but 
still  more  by  the  formation  of  crusts  of  salts  on  the  inside  of  the  vessel. 
In  cases  where  salt  separates  out,  stirring  must  be  effected  con- 
tinuously, and  the  stirrer  must  approach  the  walls  as  closely  as 
possible,  in  order  to  keep  these  scraped  clean.  If,  however,  large 
quantities  of  salt  have  separated  out  no  amount  of  stirring  will  be  of 
any  use.  A  case  is  known  to  the  writer  where,  owing  to  the  formation 
of  a  crust  of  salt  only  4  cms.  thick,  an  autoclave  became  heated  up  to 
redness,  and  with  an  internal  temperature  of  240°  and  a  pressure  of 
48  atmos.,  blew  out  like  a  balloon,  after  which  the  bottom  split  open. 
The  issuing  stream  of  vapours  cooled  the  steel  sufficiently  to  prevent 
any  further  danger.  It  is  quite  certain  that  if  cast  iron  had  been  used 
it  would  have  exploded.1 

For  the  reasons  just  given,  it  is  always  desirable  to  heat  the 
autoclave,  whenever  possible,  in  a  suitable  bath.  Such  a  bath  may 
contain  either  oil  or  solder.  Even  when  no  crusts  are  formed,  which 
would  interfere  with  the  heat  transference,  phenomena  occur  at 
higher  temperatures,  which  render  the  use  of  a  solder-bath  very 
desirable.  The  solder  which  is  poured  in  to  fix  the  liner  in  position 
always  liquefies  if  the  autoclave  is  heated  directly,  and  the  liner  rises 
up  until  finally  it  touches  the  cover,  and  so,  after  cooling,  renders  it 
difficult  to  screw  the  cover  down  tightly  again  when  closing  the  vessel. 
In  this  way  strains  are  developed  in  course  of  time  which  make  the 
autoclave  leaky,  and,  in  addition,  the  strain  on  the  bolts  is  a  serious 

1  The  /?-naphthol  melt  is  an  example  of  this  type,  and  any  attempt  to  carry 
out  this  melt  without  the  use  of  a  metal  bath  will  with  certainty  ruin  any  autoclave. 


196  TECHNICAL   DETAILS 

source  of  danger.  With  incorrect  heating  not  only  does  the  autoclave 
itself  suffer,  but  also  the  substances  which  are  being  heated  ;  such 
cases  have  been  discussed  in  detail  in  connection  with  a-naphthol 
and  /3-naphthylamine. 

The  autoclave  is  charged  either  through  the  man-hole,  this  being 
then  carefully  closed,  or,  if  possible,  the  substance  is  sucked  in  by 
evacuating  the  vessel  so  that  as  little  opportunity  as  possible  may  be 
given  for  the  development  of  leaks.  Water  expands  very  considerably 
upon  heating  (according  to  Mendeleef  by  20  %  of  its  volume  on 
heating  from  0-250°),  for  which  reason  no  autoclave  should  be  rilled 
up  to  more  than  80  %  of  its  total  volume.  If  the  vessel  is  completely 
rilled  such  an  enormous  pressure  will  be  developed  that  it  will  be 
burst  open.  It  is  therefore  necessary  to  have  a  notice  above  every 
autoclave,  showing  clearly  the  total  volume,  the  maximum  pressure, 
the  maximum  filling,  and  the  method  of  charging. 

The  calculations  for  an  autoclave  are  matters  for  engineers  who 
have  official  standards  upon  which  to  base  their  estimates.  It  is, 
however,  also  advisable  to  have  every  apparatus  recalculated  in  a 
first-class  engineering  works,  after  which  the  official  sanction  for  the 
scheme  may  be  applied  for. 

By  means  of  a  travelling  crane  the  autoclave  is  placed  in  its 
masonry  setting,  which  has  already  been  erected,  and  which  should  be 
held  down  by  means  of  iron  rods  placed  about  30  cms.  apart,  the 
projecting  ends  being  screwed  down  to  the  brickwork  by  means  of 
iron  plates  25  by  25  cms.  square.  The  autoclave  or  its  bath  is  placed 
in  a  counter-sunk  ring,  as  shown  at  the  bottom  of  Fig.  32,  and  the 
apparatus,  after  being  charged,  is  heated  up  by  means  of  good  coal. 
If  the  setting  has  been  correctly  done,  it  is  unnecessary  to  carry  out 
the  first  heating  with  excessive  caution,  although  it  is  always  advisable 
to  start  with  a  small  flame.  The  fire-bars  must  be  kept  clear,  and, 
if  necessary,  one  or  more  should  be  removed  if  the  draught  is  in- 
sufficient. It  is  also  advisable  to  have  a  separate  chimney  for  each 
pair  of  large  autoclaves,  so  as  to  be  independent  of  neighbouring 
plant.  When  working  on  the  large  scale  the  heating-up  always 
occupies  several  hours,  but  once  the  brickwork  is  hot  a  very  little 
wood  or  coal  will  suffice  to  keep  the  temperature  up.  For  tempera- 
tures above  200°  the  heat  losses  by  radiation  are  so  considerable  that 
the  portion  of  the  apparatus  projecting  from  above  must  be  insulated 
by  means  of  a  tin  cover  lined  with  asbestos.  To  cool,  the  cover,  which 
is  made  in  several  pieces,  is  removed,  and  at  the  same  time  the 
furnace  door  and  the  dampers  are  opened.  By  blowing  off  a  portion 
of  the  contents  into  the  air,  or  in  the  cases  of  alcohol  and  ammonia, 


CONSTRUCTION  AND   USE   OF  AUTOCLAVES     197 

into  the  condenser,  the  cooling  of  the  autoclave  may  be  greatly 
accelerated  without  the  brickwork  losing  too  much  heat,  which  is  of 
importance  for  the  next  operation.  Whilst  a  melt  is  being  carried 
out  the  autoclave  must  be  carefully  watched.  The  temperature 
of  the  oil-bath  should  be  about  30°  higher  than  the  internal  tempera- 
ture, and  the  two  thermometers  and  manometers  should  agree 
within  a  couple  of  points.  If  greater  deviations  are  shown,  the 
thermometers  must  be  checked,  and  in  some  cases  the  process  must 
be  interrupted. 

By  the  use  of  pyrometers  it  is  possible  to  superintend  the  running 
of  a  process  from  the  laboratory,  and  self-registering  manometers 
are  coming  into  use  which  permit  of  the  subsequent  examination 
of  the  pressures  for  purposes  of  control.  A  book  should  be  kept  in 
which  all  happenings  are  entered,  so  that  documentary  proof  is 
always  available  in  case  of  a  break- down  or  an  accident.  If,  in  spite 
of  all  precautions,  any  serious  mishap  should  occur, .  such  as  an 
unexpected  rise  of  the  temperature  or  pressure,  the  fire  must  be 
raked  out  at  once,  all  the  dampers  and  flues  should  be  opened,  and 
all  the  personnel  should  be  evacuated  from  the  shed  in  which  the 
autoclave  is  situated  and  from  the  surrounding  buildings.  The 
explosion  of  an  autoclave,  like  one  of  those  shown  in  Figs.  31  and  32, 
may  lay  an  entire  factory  in  ruins.  Since,  however,  all  autoclaves 
are  made  with  an  eight-fold  factor  of  safety,  there  is  really  no  danger 
with  proper  attention.  Every  year  each  autoclave  is  examined  by  a 
boiler  inspector,  being  cleaned  out  and  well  cooled  for  the  purpose. 
The  inside  of  such  a  vessel  must  not  be  entered  until  it  has  been 
shown  that  a  candle  can  burn  quietly  therein.  Usually  only  the 
man-hole  is  open,  and  compressed  air  is  blown  in.  Never  less  than 
two  workmen  should  be  engaged  upon  the  job.  The  result  of  the 
examination  should  be  made  the  subject  of  an  official  report.  Fre- 
quently the  lining  is  removed  in  order  that  any  alterations  in  the  wall 
may  be  accurately  measured  ;  the  liner  is  removed  for  the  purposes 
of  the  examination  by  lighting  a  fire  inside,  which  is  kept  going  by 
means  of  compressed  air.  As  soon  as  the  lead  is  molten  the  liner 
rises  up  somewhat  and  is  then  removed  by  means  of  the  crane.  The 
lead  is  removed  by  means  of  iron  ladles  and  is  cast  into  bars. 

Autoclaves  are  generally  erected  in  tall,  well-lighted  sheds 
provided  with  a  travelling  crane.  Plate  VII  shows  in  section  the 
interior  of  a  colour  shed  with  the  adjoining  autoclave  shed.  It  may 
be  seen  from  this  how  the  materials  are  brought  to  the  vessel,  and 
how  the  finished  product  is  blown  over  directly  into  the  intermediate 
shed. 


198  TECHNICAL   DETAILS 

Laboratory  Autoclaves  are  constructed  on  precisely  similar 
lines  to  those  used  in  the  works.  The  diagrams  on  Plates  I  and  X 
show  two  vessels  made  from  cast  steel  with  and  without  stirring 
gear.  Plate  XIII  also  shows  all  the  details  of  a  properly  constructed 
stir  ring- autoclave.  As  already  mentioned,  the  liner  must  be  very 
carefully  fixed  in  by  means  of  solder.  If  a  solder-bath  be  used 
instead  of  oil,  an  iron  bath  must  be  provided,  as  copper  is  attacked  by 
the  lead.  In  the  laboratory  the  stuffing-box  is  not  usually  cooled, 
as  the  loss  by  possible  blowing  off  is  very  slight  ;  it  is  only  advisable 
to  cool  where  high  pressures  and  temperatures  are  encountered,  but 
for  such  cases  it  is  preferable  to  use  the  rotating  autoclave  already 
described.  Attention  may  be  called  to  the  fact  that  the  stirrer  should 
always  work  clockwise,  to  avoid  unscrewing  the  nut  of  the  stuffing-box. 
The  nuts  which  close  the  autoclave  are  tightened  carefully  and 
regularly  in  the  laboratory,  just  as  is  done  on  the  large  plant,  with  the 
difference,  however,  that  it  is  inadvisable  to  tighten  up  the  nuts 
with  a  hammer,  as  they  may  be  broken  off.  It  suffices  to  tighten  up 
by  means  of  a  long  spanner,  the  autoclave  being  placed  in  a  stand 
which  will  prevent  it  rotating. 

The  cover  may  be  either  dome-shaped  or  flat,  as  may  be  seen 
from  the  sectional  diagram  of  Fig.  34  and  from  Plates  I,  XIII,  and 
XIV,  Fig.  35.  The  flat  top  is  to  be  preferred  as  it  is  easier  to  screw 
the  agitator  bracket  down  to  it  firmly,  and  the  flange-pipes  can  more 
easily  be  rendered  air-tight.  The  vertical  autoclave  shown  on 
Plate  XIV,  Fig.  35,  has  a  domed  cover  with  flange-pieces  for  affixing 
the  various  fittings. 

The  heating  is  done  by  means  of  a  Fletcher  burner,  and,  later, 
it  may  be  done  with  a  good  Bunsen  burner  directly  under  the  middle, 
but  not  by  several  burners  on  different  sides.  The  autoclave  must 
be  protected  from  draughts  and  be  insulated  by  a  tin  cover,  about 
70  %  of  gas  being  saved  in  this  way.  In  order  to  cool,  the  whole 
apparatus  is  removed  from  the  bath  and  is  stood  on  an  iron  triangle, 
so  that  the  oil  may  run  back  into  the  bath.  Heating  and  cooling 
will  occupy  only  about  an  hour.  In  the  event  of  anything  unforeseen 
occurring  the  same  rules  apply  as  on  the  large  scale,  making  due 
allowances  for  the  different  circumstances.  The  screws  must  not 
be  loosened  so  long  as  there  is  any  pressure,  but  that  on  the  stuffing- 
box  may  be  moved  without  danger.  For  the  rest,  attention  is  called 
to  the  general  rules  given  below. 

Instead  of -using  an  enamelled  liner,  it  is  also  possible  to  have  the 
cover  and  the  inside  of  a  laboratory  autoclave  enamelled  directly, 
but  there  are  few  factories  which  do  this  satisfactorily.  The  cost 


CONSTRUCTION  AND   USE   OF  AUTOCLAVES     199 


FIG.  34. — Section  through  a  laboratory  autoclave. 

A.  Stuffing-box.     B.  Packing.     C.  Oil-bath.     D.  Cast-steel  vessel.     E.  Lead. 

F.  Liner. 


200  TECHNICAL   DETAILS 

of  the  enamelling  is  calculated  according  to  the  weight  of  the 
apparatus. 

In  those  cases  where  it  is  necessary  to  carry  out  an  operation  under 
pressure  in  the  laboratory  with  stirring,  considerable  difficulties  are 
found  when  pressures  of  about  20  atmos.  are  reached,  as  it  is  necessary 
to  tighten  up  the  stuffing-box  and  also  to  cool  it.  For  this  reason 
I  have  made  use  for  many  years  of  a  piece  of  apparatus  which  is 
similar  in  construction  to  the  known  form,  but  has  also  certain  novel 
features.  Plate  XV,  Fig.  37,  shows  such  a  rotating  autoclave  in 
use,  and  Fig.  38  shows  it  in  section. 

The  opening  is  contracted  so  that  as  few  bolts  as  possible  may  be 
required,  the  whole  vessel  being  turned  in  one  piece  from  an  old 
wrought-iron  printing  roller.  In  order  that  the  pressure  and  the 
temperature  may  be  measured,  the  apparatus  is  arranged  diagonally, 
and  the  angle  of  inclination  may  be  altered  as  desired.  The  top 
opening  is  utilized  for  the  manometer,  and  the  bottom  for  the  thermo- 
meter, which  is  fixed  in  by  means  of  asbestos  paper.  The  weight  of 
the  autoclave  does  not  rest  upon  the  axle  of  the  worm-drive,  but  is 
taken  up  by  a  bronze  stuffing-box  which  is  attached  to  the  supporting 
columns.  For  this  reason  surprisingly  little  power  is  required  to 
drive  it.  For  a  content  of  400  c.cs.  the  apparatus  weighs  n  kilos., 
and  is  constructed  to  stand  100  atmos.  pressure  ;  the  stand  weighs 
as  much  again.  Whilst  it  is  being  heated,  the  cylinder  is  covered  with 
a  tin  cover,  so  that  less  than  20  %  of  the  gas  is  needed  which  would 
be  required  by  any  other  form  of  autoclave.  Experiments  made 
with  a  view  to  replacing  the  expensive  bolts  and  nuts  by  a  simple 
screw  fastening  have  met  with  no  success,  as  at  about  180°  the  screw 
packing  always  blows  out.  The  packing  simply  sticks  to  the  cover 
on  screwing  up,  and  it  is  impossible  to  make  the  apparatus  tight. 


General  Rules  for  the  Use  of  Autoclaves. 

1.  The  packing  ring  must  always  be  clean. 

2.  Tightening  up  must  always  be  done  at  diametrically  opposite 
points  by  first  screwing  up  the  bolts  gently,  and  then  tightening  up 
by  working  round  in  a  circle. 

3.  If  neutral  or  similar  liquids  are  heated,   which  evolve  no 
ammonia,  manometers  fitted  with  bronze  tubes  may  be  used.     If, 
however,  vapours  are  given  off  which  attack  copper  or  bronze,  a 
steel  tube  manometer  must  be  used,  as  copper  and  bronze  are  soon 
destroyed. 

4.  A  liner  fixed  in  position  by  means  of  solder  must  always  be 


CONSTRUCTION  AND  USE  OF  AUTOCLAVES    201 


FIG.  38. — Section  through  rotating  autoclave. 

± 


I  i       I       I          I  i 

\ — [-4-1— j-  h— rtt-  - 

Gi  i !  i       i       A.     i 


FIG.  38A. — Details  of  rotating  autoclave. 

A.  Frame  supporting  autoclave.     B.  Hinge.     C.  Bronze  bushing  for  axle.     D.  Worm  shaft. 
E.  Collar.     F.  Oil-hole.     G.  Bronze  pulley-wheel. 


202 


TECHNICAL    DETAILS 


used  ;  any  solder  which  is  squeezed  out  being  replaced.  Only 
under  quite  special  conditions  can  the  use  of  a  liner  be  dispensed 
with. 

5.  The  temperature  must  be  measured  both  inside  and  in  the 
oil-  or  metal-bath,  the  latter  temperature  being  about  25°  higher  than 
the  former. 


360'  C. 


Temperature-pressure  curve  for  aqueous  caustic  soda. 


6.  The  autoclave  must  be  protected  from  draughts,  for  which 
purpose  it  should  be  insulated  and,  on  the  large  scale,  provided  with  a 
cover. 

7.  If  the  vessel  is  found  to  leak,  the  experiments  must  be  stopped. 
The  screws  must  not  be  tightened  so  long  as  there  is  any  pressure  ; 
the  stuffing-box,  however,  may  safely  be  tightened  up  during  the 
course  of  the  process. 

8.  An  autoclave  may  only  be  opened  after  the  pressure  has  been 


STRUCTURAL   MATERIALS  203 

blown  off,  as  the  manometer  often  fails  to  indicate  a  pressure,  although 
it  may  be  present. 

9.  Neither  the  vessel  nor  the  oil-bath  may  ever  be  completely 
filled,  as  both  water  and  oil  expand  very  considerably  on  heating.    If 
the  vessel  is  completely  full  it  is  certain  to  burst. 

10.  Every   autoclave   should   be    officially   examined   annually, 
tested,  and  a  report  made  on  its  condition.     The  date  of  examination 
should  be  stamped  on  the  vessel .     Both  the  capacity  and  the  maximum 
pressure  allowable  should  also  be  marked. 

11.  Works  autoclaves  should  be  thoroughly  cleaned  out,  cooled, 
and  provided  with  a  ventilating  tube  before  the  examination. 

12.  The  stonework  for  a  works  autoclave  should  first  be  erected 
on  firm  foundations,  and  then  the  complete  autoclave  should  be 
lowered  into  it.     After  it  has  been  mounted  the  apparatus  should  at 
once  be  ready  for  use. 


13.  STRUCTURAL  MATERIALS  USED  IN  DYE  CHEMISTRY. 

The  destructive  action  of  chemicals  makes  the  nature  of  the 
structural  material  used  in  the  dye  industry  a  matter  of  prime 
importance.  From  time  to  time  it  becomes  necessary  to  decide 
what  material  is  to  be  used,  and  experience,  or,  if  one  may  say  so, 
chemical  instinct,  must  be  called  upon  for  guidance. 

The  materials  used  in  colour  technology  may  be  divided  into 
Inorganic  and  Organic.  The  Inorganic  may  be  subdivided  into 
Metals  and  Non-metals,  and  the  Organic  into  Natural  and 
Artificial. 

i.  Metals. 

Iron  is  the  most  important  structural  material  used  in  dye 
chemistry,  and  is  utilized  in  every  variety  and  form. 

In  the  form  of  cast  iron  it  is  used  for  sulphonating-  and  nitrating- 
pots,  for  evaporating  plant,  cocks,  stirring-gear,  autoclaves,  and,  in 
short,  wherever  the  liquids  dealt  with  are  neutral  or  alkaline. 
The  insufficient  tensile  strength  of  this  excellent  and  easily  cast  metal 
alone  prevents  its  still  wider  use. 

As  is  well  known,  the  properties  of  cast  iron  vary  considerably 
according  to  its  chemical  composition.  For  acid-resistant  cast  iron, 
that  is  to  say,  such  as  is  little  attacked  by  concentrated  acids,  ordinary 
grey  cast  iron  is  made  use  of,  its  resistance  being  improved  by 
certain  additions  which  are  kept  a  secret  by  the  various  foundries. 


204  TECHNICAL   DETAILS 

Ordinary  grey  cast  iron  answers  all  requirements  when  dealing  with 
sulphuric  acid  of  at  least  75  %  strength,  nitric  acid,  or  mixtures  of 
the  two.  It  becomes  passive,  and  so  acquires  quite  a  fair  resistance 
even  to  moderately  dilute  acids.  It  never  does,  however,  to  trust  to 
luck  in  these  cases,  and  experiment  alone  can  decide  whether  grey 
cast  iron  will  do  in  a  given  case.  Further,  the  vessel  must  be  carefully 
cleaned  out  after  every  stoppage.  Grey  cast  iron  vessels  must  be 
washed  out  when  a  manufacture  is  stopped,  traces  of  acid  removed 
with  boiling  soda  solution,  the  washing  water  blown  out  at  the  boiling- 
point,  and  the  small  remainder  swabbed  out  so  that  the  vessel  is 
completely  dry.  If  the  pot  stands  in  a  wooden  water-bath,  then  the 
latter  must  be  kept  filled  to  prevent  shrinkage,  and  the  water  should 
be  made  strongly  alkaline  by  means  of  soda  to  prevent  it  becoming 
foul. 

Further,  the  agitator  brackets  of  vats,  autoclaves,  and  other 
vessels  are  constructed  from  grey  cast  iron.  To  ensure  easy  running 
the  toothed  wheels  should  be  well  oiled,  and  it  is  also  very  advisable 
for  all  larger  pieces  of  apparatus  to  be  mounted  on  ball-bearings 
whenever  possible,  as  by  this  means  a  considerable  saving  of  power 
and  lubricant  is  effected.  The  stands  and  end-pieces  of  filter- 
presses  are  made  of  cast  iron,  but  not  the  tie-rods,  as  cast  iron  has 
not  sufficient  tensile  strength  for  this  purpose.  Autoclaves  may  be 
made  from  cast  iron  for  working  up  to  40  atmos.,  but  for  higher 
pressures  cast  steel  must  b'e  used,  as  cast  iron  is  liable  to  contain 
blow-holes  when  used  on  too  large  a  scale  and,  further,  the  walls 
required  would  be  far  too  thick.  The  autoclave  shown  on  Plate  XII 
(Fig.  32),  constructed  of  cast  steel,  has  walls  80  mms.  thick,  and 
weighs  10  tons  ;  to  construct  a  vessel  of  similar  capacity  with  a 
diameter  1*2  metres  of  cast  iron,  and  capable  of  withstanding  a 
working  pressure  of  40  atmos.,  it  would  be  necessary  to  make  the 
walls  400  mms.  thick,  and  its  weight  would  be  over  60  tons.  Such  a 
freak  apparatus  could  not  in  any  case  be  used  technically,  owing  to 
the  enormous  tension  which  would  be  produced  on  heating.  The 
fusion-pots  for  the  manufacture  of  naphthol  are  also  made  of  grey 
cast  iron,  and  it  has  been  found  that  the  addition  of  1-3  %  nickel 
increases  the  resistance  to  alkali  to  a  remarkable  extent ;  fused  alkali, 
especially  caustic  potash,  attacks  iron  very  strongly. 

A  type  of  cast  iron  which  is  completely,  or  almost  completely, 
unattacked  by  acids  has  been  on  the  market  fairly  recently  in  the  form 
of  alloys  containing  about  12  %  of  silicon  and  4-6  %  aluminium. 
This  ferro-aluminium  silicon  alloy  is,  however,  somewhat  strongly 
attacked  by  hydrochloric  acid  ;  it  was  first  made  use  of  in  England 


STRUCTURAL  MATERIALS  205 

under  the  names  of  Ironac  and  Tantiron  ;  there  are  also  certain 
imitations  known  as  Kieselguss,  Azidur,  and  Clusiron,  which  can  all 
be  cast  very  easily  but  are  unfortunately  glass-hard  and  brittle,  so 
that  they  have  to  be  worked  with  an  emery  wheel.  For  nitric  acid 
distilling  plants  these  alloys  serve  excellently,  and  they  also  form  a 
welcome  addition  to  the  list  of  materials  available  for  various  other 
special  purposes,  but  they  cannot  be  used  for  the  linings  for  auto- 
claves owing  to  their  brittleness. 

Where  great  strength  is  necessary,  wrought  iron,  ingot  iron,  and 
steel  must  be  used.  These  forms  of  iron  are  used  for  the  tie-rods 
of  filter-  and  hydraulic-presses.  The  head-pieces  of  the  latter  must 
be  made  of  cast  steel,  as  cast  iron  has  not  sufficient  strength.  In 
recent  years  also  Swiss  electric  steel  has  been  used.  Steel  is  also 
used  for  the  spiral  tubes  of  spring  manometers  where  ammonia  is 
dealt  with.  Ingot  iron  is  employed  for  the  hoops  of  vats. 

Formerly,  rather  more  use  was  made  of  copper  than  at  present,  but 
even  to-day  it  is  quite  indispensable.  It  is  used  for  scoops  (but  not 
for  ordinary  diazotizations),  for  the  baskets  of  centrifuges,  for  piping, 
and,  in  particular,  for  drying  trays,  where  it  is  used  almost  exclusively. 
It  is  not  resistant  towards  ammonia  admixed  with  air,  and  is  often 
tinned  in  order  to  protect  it.  Alcohol  stills  are  usually  made  of 
copper. 

Tin  is  hardly  used  at  all  as  such,  but  only  in  the  form  of  alloys, 
such  as  bronze,  lead-tin  alloy  for  filling  baths,1  and,  especially,  for 
tinning  iron  and  copper  vessels  2  (see  homogeneous  lead  coverings). 

Zinc,  also,  is  rarely  used  as  such,  but  chiefly  in  the  form  of  brass 
and  bearing-metal  alloys,  and  also  as  the  coating  of  the  so-called 
"  galvanized  iron." 

Aluminium,  on  the  contrary,  owing  to  its  great  resistance  towards 
dilute  and  concentrated  nitric  acid,  is  coming  more  and  more  into 
use.  It  is  frequently  met  with  in  the  form  of  piping  for  nitric  acid 
and  for  nitrating  pots,  but  it  has  the  disadvantage  of  offering  only  a 
poor  resistance  to  factory  air. 

Nickel  is  hardly  ever  used  except  in  special  alloys. 

Of  other  metals  than  iron,  lead  is  by  far  the  most  important,  and 
is  quite  indispensable.  It  is  found  in  nearly  all  filter-presses  in  the 
form  of  lead  tubes,  and  also  for  other  piping  which  has  to  deal  with 
acid  and  alkaline  liquids.  The  head-pieces  of  the  filter-presses  are 
covered  with  sheet-lead,  as  also  are  the  inlet  tubes.  It  is  often  found 

1  An  alloy  made  with  equal  parts  of  lead  and  tin  does  not  expand  at  all,  practi- 
cally speaking,  on  heating. 

2  The  inlet-pipes   of  filter-presses,  and  also  the  cocks  of  colour  vats,   are 
practically  always  made  from  the  best  quality  bronze. 


206  TECHNICAL  DETAILS 

on  heating  metal  which  has  been  covered  with  lead  that  the  latter 
becomes  loose,  develops  large  blisters,  and  finally  breaks  away.  This 
disadvantage  is  overcome  by  fusing  or  alloying  the  lead  covering 
to  the  metal  beneath,  instead  of  merely  laying  it  on.  Apparatus 
which  has  been  covered  with  an  intimate  coating  of  lead  in  this  way 
is  said  to  be  homogeneously  lead-lined  ;  this  homogeneous  lead  covering 
is  playing  an  increasingly  important  part  in  colour  technology. 
Circular  apparatus  such  as  the  lining  for  autoclaves,  and  so  on,  is 
lead-lined  according  to  the  method  of  Kuhnle  Kopp  and  Kausch  by 
rotating  the  vessel  rapidly  and  then  pouring  in  lead.  In  this  way  all 
the  pores  of  the  metal  are  completely  closed,  and  it  is  possible  to  deal 
with  plant  up  to  6000  litres  and  weighing  up  to  10  tons.  Iron  and 
copper,  before  being  treated  in  this  manner,  must  first  be  tinned, 
otherwise  the  coating  does  not  adhere  well.  This  layer  is  often  quite 
thick,  2  mms.  and  more,  so  that  several  thousand  kilograms  may  be 
required  for  a  large  piece  of  apparatus. 

These  short  notes  do  not,  of  course,  in  any  way  exhaust  the  uses 
of  metals  in  the  dye  industry,  but  they  suffice  to  show  what  a  large 
part  is  played  by  these  structural  materials  in  the  industry. 

2.  Non-Metals. 

The  most  important  of  the  inorganic  materials  are  cement  and 
stoneware. 

Where  complete  resistance  to  acid  is  required,  stoneware  is  the 
only  material  which  can  be  used.  Occasionally,  indeed,  its  place 
may  be  taken  by  lead,  but,  as  every  works  chemist  finds  out  in 
course  of  time,  even  with  the  most  careful  lead-lining,  expensive 
repairs  become  necessary  sooner  or  later.  If  a  plant  has  to  be  used 
for  an  indefinite  length  of  time  without  interruption,  stoneware  must 
be  used  or,  very  occasionally,  acid-resistant  stone,  such  as  volvic 
lava,  granacite,  or  Binger  sandstone. 

For  smaller-sized  plant,  taps  made  of  stoneware  are  much  used, 
and  with  careful  treatment  they  will  last  indefinitely.  They  are 
liable,  however,  to  be  damaged  by  hot  liquids  owing  to  cracking  ; 
they  must  also  be  carefully  lubricated  to  avoid  sticking.  The  so- 
called  armoured  stoneware  cocks  are  more  resistant  to  shock  and 
heat ;  the  outside  consists  of  lead-lined  tin-plate  which  is  usually 
tightened  up  by  means  of  a  screw,  so  that  by  loosening  the  latter 
slightly  the  tap  is  readily  removed.  These  armoured  taps  have 
quite  replaced  the  older  type  made  of  hard  lead  (lead- antimony). 
Stoneware  is  also  used  for  piping,  centrifuges  and  valves.  The 


STRUCTURAL   MATERIALS  207 

baskets  of  stoneware  centrifuges  are  placed  inside  a  steel  basket  to 
prevent  them  flying  to  pieces  owing  to  the  centrifugal  force.  Some 
of  the  pieces  of  apparatus  made  are  very  complex,  but  we  cannot 
go  further  into  this  question  here  ;  details  will  be  found  in  the 
catalogues  issued  by  the  stoneware  manufacturers. 

Stoneware  reservoirs  are  much  used  which  are  either  made  in 
one  piece'  or  built  up  from  separate  pieces.  Complete  vessels  may 
be  prepared  up  to  5000  litres  capacity,  but  they  are  very  sensitive  to 
slight  variations  in  temperature  and  are  also  expensive.  Acid- 
resistant  tanks  can  be  constructed  in  the  factory  if  a  good  bricklayer 
is  available  :  an  iron  pot  is  covered  with  a  layer  of  cement,  and  when 
this  is  dry  a  layer  of  acid-proof  bricks,  or  glazed  stoneware  plates,  is 
fixed  to  it  by  means  of  ordinary  cement.  The  individual  plates 
must  be  set  6  mms.  apart  from  one  another ;  the  resultant  grooves 
are  filled  up  with  acid-proof  cement,  which  is  obtainable  in  excellent 
quality  from  various  firms.  The  grooves  are  first  half-filled  with  the 
aid  of  a  thin  wooden  spatula,  and  the  cement  is  dried  by  heating  the 
whole  apparatus  with  a  steam  coil,  which  takes  about  14  days.  Only 
when  the  first  layer  of  the  acid-proof  cement  is  quite  dry  are  the 
grooves  completely  filled  up  and  again  dried.  The  complete 
preparation  of  such  a  tank  holding  5000  litres  takes  about  2  months. 
When  the  cement  has  set,  the  vessel  is  filled  with  2  %  sulphuric  acid 
and  allowed  to  stand  for  three  days.  By  this  means  the  acid-proof 
cement  is  hardened,  and  there  is  no  danger  of  the  grooves  developing 
leaks.  When  properly  prepared,  such  a  vessel  will  withstand  even 
hot  80  %  sulphuric  acid,  and  can  be  guaranteed  to  stand  pressure 
and  vacuum.  Vessels  are  also  made  with  two  layers  of  acid-proof 
tiles  in  which  the  grooves  are  so  arranged  that  the  first  set  of  grooves 
are  covered  by  the  second  tiles.  They  are,  however,  very  expensive, 
and  last  hardly  any  longer  than  a  tank  with  a  single  layer  when 
properly  made. 

Alkaline  and  neutral  liquids  may  be  kept  in  cement  reservoirs 
which  are  frequently  reinforced  with  iron.  As  enormous  tensions 
are  developed  on  heating,  the  reinforcing  must  be  carefully  calculated. 
Cement  vats  are  also  used  for  the  manufacture  of  colours,  but  it  is 
advisable  to  line  such  vats  also  with  acid-proof  tiles  as  even  quite 
weak  acids  rapidly  corrode  the  cement.  Cement  stirrers  can  also 
be  made  and  are  very  useful  in  special  cases. 

The  floors  of  works  sheds  may  be  covered  with  a  layer  of  acid- 
proof  tiles  cemented  together  with  sulphur  ;  this  adheres  firmly  to 
the  tiles  and  is  not,  like  asphalt,  washed  away  by  hot  water.  In 
sheds  where  the  floor  keeps  dry  a  good  cement  surface  is  sufficient. 


208  TECHNICAL   DETAILS 

Glass,  owing  to  its  brittleness,  is  used  relatively  little,  but  often 
there  is  no  alternative.  For  chlorinations  at  high  temperatures,  for 
instance,  it  is  indispensable  (see  also  Dichlorbenzaldehyde).  Tubing 
for  conveying  chlorine  is  often  of  glass,  and  glass  stirrers  are  met  with 
fairly  frequently  which  are  made  by  fixing  stout  glass  rods  into  an 
iron  or  wooden  beam.  Fused  quartz  is  little  used  as  yet,  but  quartz 
lamps  are  coming  into  favour  for  chlorinations  (cf.  p.  93). 

Porcelain  is  only  found  in  laboratories  and  dye-houses.  The 
much  vaunted  resistance  glass  vessels  burst  too  frequently  to  be 
worth  recommending. 

Enamel  is  a  particular  form  of  glass  which  is  specially  used  for 
coating  cast  iron.  The  production  of  a  good  acid-proof  enamel  is 
no  easy  matter,  and  for  works  plant  a  double  coating  is  often  applied. 
This  enamel  has  not  so  good  an  appearance  as  the  enamel  used  on 
ordinary  household  articles,  but  it  is  much  more  durable.  An 
enamelled  apparatus  which  has  developed  a  defect  at  any  point  must 
practically  always  be  dismantled,  for  which  reason  it  needs  to  be 
treated  with  great  care.  Enamelled  vessels  must  never  be  touched 
with  metal  instruments  but  only  with  wooden  implements.  Very 
complicated  pieces  of  enamelled  apparatus  are  made,  which  are 
charged  for  according  to  their  weight  and  are  very  expensive. 
Enamelled  ladles  and  pots  are  also  much  used. 

3.  Structural  Materials  of  Organic  Origin. 

The  most  important  material  of  natural  origin  is,  of  course, 
wood.  It  is  used  for  the  vats  employed  in  the  manufacture  of 
colours,  for  agitators,  scaffolding,  and,  above  all,  for  the  construction 
of  the  sheds  themselves.  In  recent  years  the  place  of  wooden 
buildings  has  begun  to  be  taken  by  reinforced  concrete,  but  it  remains 
to  be  seen  how  this  lasts.  Wood  is  surprisingly  resistant  to  all 
chemicals,  as  it  is  only  attacked  on  the  surface,  and  this  damaged  layer 
serves  to  protect  the  material  beneath. 

In  the  first  place  comes  American  pitch-pine,  together  with  larch 
and  pinewood.  Beech  cannot  be  used  owing  to  the  large  cracks,  but 
oak  vats  are  often  found,  which  are  expensive  but  very  resistant. 
Other  woods,  with  the  exception  of  ash,  are  not  used  owing  to  their 
high  price. 

Vats  are  made  of  capacities  of  20,000  litres  ;  the  stirrers  are  made 
of  ash  and  are  fixed  to  the  stirring  gear  by  means  of  wrought  iron 
collars  (see  also  under  cast  iron).  Vats  of  these  dimensions  are 
seldom  placed  on  a  platform,  as  shown  on  Plate  VII,  but  are  usually 


PLATE  XVII. 


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STRUCTURAL    MATERIALS  209 

stood  directly  on  the  ground.  The  pressure  boiler  is  either  sunk 
in  the  ground  or  else  is  stood  by  its  side,  and  the  liquid  sucked  out 
by  vacuum. 

If  a  tub  is  to  be  evacuated  it  must  be  strengthened  internally 
with  a  cross-beam  ;  further,  to  prevent  it  from  flying  to  pieces  on 
applying  a  pressure  of  2-3  atmos.  it  must  be  strengthened  by  means 
of  strong  iron  bars.  In  addition  to  the  syphon  tube,  a  small  air  tube 
is  also  fitted  so  that  the  suspensions  of  the  precipitated  dye  may  be 
kept  stirred  up  by  means  of  compressed  air.  If  this  precaution  is 
not  observed  it  may  happen  that  a  large  portion  of  the  colour  remains 
at  the  bottom  of  the  tub.  All  iron  bands  must  be  carefully  painted 
with  red  lead,  and  often  the  whole  vat  is  covered  with  it.  If  the 
liquid  in  the  tub  is  to  be  heated  to  boiling  it  must  be  covered  in  to 
prevent  the  steam  from  escaping  and  as  a  precaution  against  accidents  ; 
a  proper  steam  waste-pipe  is  also  necessary,  as  shown  clearly  on 
Plate  VII.  Steam  flues  are  provided  with  an  air  or  steam  tube  with 
which  a  powerful  draught  can  be  created. 

The  chambers  and  frames  of  filter-presses  are  made  of  wood, 
and  where  alkaline  liquids  are  to  be  dealt  with  larch,  or,  better,  oak, 
is  used  in  place  of  the  resinous  pitch-pine.  For  filter-press  taps 
small  pear-wood  faucets  are  made  use  of. 

Leather  is  used  for  driving  bands,  for  the  leather  collars  of 
hydraulic  presses  and  other  less  important  purposes. 

Rubber  is  the  most  important  of  the  artificial  organic  materials. 
It  is  used  in  many  forms,  such  as  tubing,  as  hard  rubber  for  covering 
centrifuges,  ladles,  and  taps.  The  rubber  coatings  of  centrifuges 
last  very  well,  but  are  rarely  used  in  dye  chemistry.  Gallic  acid  is 
"  whizzed  "  in  them,  but  copper  baskets,  and  even  baskets  coated 
with  lead  by  Schoop's  process,  can  often  be  used. 

Manufactured  organic  substances  are  represented  by  filter  cloths, 
which  are  made  from  cotton,  jute,  hemp,  and  wool.  Filter-press 
cloths  are  usually  made  of  cotton,  wool  being  rarely  used.  Strongly 
acid  precipitates  are  pressed  in  camel-hair  cloths  ;  for  some  time 
cloths  made  from  Chinese  pig- tails  were  in  use,  which  exceed  all 
others  for  durability.  The  so-called  nitro-filters  are  much  used  as 
filter-cloths,  but  not  in  filter-presses,  as  they  have  only  a  very  moderate 
degree  of  mechanical  strength.  These  are  always  prepared  from  a 
special  type  of  filter-cloth,  and  since  the  cotton  shrinks  on  nitration 
the  warp  and  woof  must  be  of  equal  strength.  Acid-resistant 
filters  can  be  made  only  in  the  following  manner  :  the  dry,  crude 
cotton  filter  is  lightly  stretched  on  an  aluminium  frame,  and  is  dipped 
into  85-88  %  nitric  acid  at  15-20° ;  it  is  then  left  in  66°  Be.  sulphuric 

H 


210  TECHNICAL   DETAILS 

acid  for  20  minutes,  after  which  it  is  thoroughly  washed.  Such 
filters  can  stand  the  action  even  of  60  %  sulphuric  acid  at  100°, 
but  they  are  at  once  destroyed  by  acid  solutions  of  ferrous  salts. 


14.    TECHNICAL  NOTES   ON   WORKS  MANAGEMENT 

As  compared  with  other  industries,  the  value  of  the  entire  world- 
production  of  dyes  is  very  slight,  its  worth  in  1913,  £20,000,000,  not 
equalling  a  tenth  part  of  the  value  of  the  wool  crop,  nor  a  fifth  of  the 
cotton  crop,  nor  a  third  of  the  rubber  crop.  The  dyes  are,  however, 
produced  under  very  severe  competition,  and  the  finished  products 
fetch  a  very  high  price.  The  energy,  intelligence,  and  perseverance 
required  for  their  manufacture  are  without  parallel  in  any  other 
industry. 

The  development  of  the  dye  industry  has  brought  it  about 
that  many  once  carefully  guarded  secrets  are  now  matters  of 
general  knowledge.  Ullmann's  great  "  Enzyklopaedie  der  Tech- 
nischen  Chemie  "  has  shown  that  many  processes  have  long  been 
known  to  most  of  the  factories.  Again,  the  migration  of  various 
workmen  has  made  it  inevitable  that  every  important  improvement 
becomes  known  to  competitors  in  a  relatively  short  time.  The 
success  of  the  great  dye  factories,  therefore,  is  not  founded  on  any 
secret  processes,  but  upon  the  traditions  of  mr.ny  years,  upon 
excellent  organization,  and  on  the  specialities  which  are  protected  by 
patents. 

It  is  a  great  mistake  to  think  that  a  colour  works  can  be  kept 
going  indefinitely  upon  specialities  alone,  and  not  only  do  young 
inexperienced  chemists  fall  into  this  error,  but  technical  experts 
and  business  men  frequently  express  this  opinion.  Specialities  are, 
so  to  speak,  the  choice  blooms  in  the  garden  of  ordinary  products, 
and  it  is  necessary  to  prepare  these  commoner,  everyday  products 
side  by  side  with  the  more  profitable  specialities.  In  order  that  a 
dye  factory  may  be  carried  on  on  a  big  scale  it  is  essential  that  the 
standard  products  should  be  made  in  the  largest  possible  quantities. 
Such  mass  products  or  staple  products  are,  first  of  all,  black  dyes 
such  as  Direct  Deep  Black  EW,  Chrome  Blacks  of  various  com- 
positions such  as  Diamond  Black  PV,  Alizarin  Black,  Erio  Chrome 
Black  T,  etc. 

Next  in  importance  to  the  black  dyes,  which  constitute  over 
50  %  of  the  total,  come  the  blue  colouring  matters,  chiefly  Indigo, 
Indanthrene,  Direct  Blue,  and  Sulphur  Blue.  After  that  come  the 


TECHNICAL   NOTES    ON   WORKS   MANAGEMENT     211 

red  dyes  such  as  Alizarin  and  Benzo  Fast  Scarlet ;  and  finally,  yellow 
products  such  as  Chrysophenine  and  Naphthamine  Yellow  NN. 

On  the  one  hand  these  standard  products  give  the  salesman  the 
opportunity  of  bringing  his  specialities  to  the  notice  of  his  customers, 
and,  on  the  other  hand,  they  tend  to  reduce  the  general  overhead 
charges  to  a  minimum.  Emphasis  has  been  laid  already  upon  the 
importance  of  recovering  all  the  by-products  produced  in  the  manu- 
facture of  intermediates,  and  it  will  be  unnecessary  to  add  more  than 
a  few  words. 

The  various  colour  factories,  recognizing  this  fact,  have  united 
together  to  form  a  so-called  "  Interessengemeinschaft,"  l  the 
members  of  which  sell  their  most  important  intermediate  products 
to  each  other  at  the  actual  cost  price,  and,  in  addition,  exchange 
information  as  to  the  methods  of  production.  Owing  to  this  concen- 
tration of  effort  it  is  possible  to  prepare  each  intermediate  product 
on  a  very  large  scale,  and  to  recover  all  by-products  such  as  nitrous 
and  sulphurous  acids,  hydrogen  sulphide,  thiosulphate,  and  Glauber 
salt,  in  the  most  rational  way.  As  a  necessary  consequence  of  this 
it  will  be  seen  that  such  a  community  of  interests  must  also  manu- 
facture their  own  inorganic  intermediates  in  order  that  they  may  be 
independent  as  regards  their  supplies  of  caustic  soda,  sulphuric  and 
hydrochloric  acids,  sodium  carbonate  and  chlorine,  and  also  common 
salt  and  coal  if  possible. 

The  plant  used  in  a  colour  factory  must  be  up-to-date,  and  the 
greatest  mistake  committed,  which  is  indeed  only  too  common, 
^  consists  in  continuing  the  use  of  badly  working,  out-of-date  apparatus. 
It  is  often  necessary  to  alter  a  plant  at  a  day's  notice  in  order  to  under- 
take some  new  manufacture,  and  it  is  the  business  of  the  super- 
intendent to  provide  as  suitable  an  apparatus  as  possible.  It  is  far 
better  to  effect  once  and  for  all  a  complete  and  fundamental  recon- 
struction of  the  plant  than  to  use  an  unsatisfactory  appliance  which 
takes  up  a  lot  of  room  and  requires  many  workmen  to  run  it.  It  is 
nearly  always  found  that  in  the  long  run  a  ruthless,  even  though 
costly,  alteration  is  really  the  cheapest.  The  calculations  are  worked 
out  by  the  Costing  Department,  which  obtains  the  requisite  data 
from  the  engineer  and  from  the  works  chemist.  In  order  that  so 
complex  a  business  as  a  dye  factory  shall  run  smoothly,  it  requires 
very  careful  organization.  The  actual  management  is  always  in 
the  hands  both  of  business  men  and  chemists,  who  divide  up  matters 
between  them  into  various  departments,  but  who  are  always  in  direct 

1  Literally="  Community  of  Interest,"  and  is  commonly  referred  to  as  the 
"  I.G." 


212  TECHNICAL  DETAILS 

contact  upon  all  important  questions.  The  commercial  director 
deals  with  the  purchase  and  sale  of  products,  whilst  the  chemical 
directorate  is  responsible  for  running  the  works,  the  research 
laboratories  and  the  dye-house.  The  so-called  "  Propaganda  Dye- 
house  "  occupies  a  more  or  less  intermediate  position,  and  deals  with 
such  current  business  as  advertising,  the  examination  of  new  colours, 
whether  of  their  own  manufacture  or  made  by  competing  firms, 
the  preparation  of  pattern  cards,  and  so  on.  The  position  of  a 
chemist  in  a  dye  factory  varies,  therefore,  very  considerably  according 
to  whether  he  is  engaged  in  the  dye-house,  in  the  research  labora- 
tories, in  the  works,  in  the  patent  department,  and  so  on.  The 
business  of  the  research  chemist  consists  in  working  out  new  scientific 
problems,  keeping  a  careful  eye  on  the  technical  literature.  Too 
much  emphasis  cannot  be  laid  upon  the  fact  that  it  is  quite  useless 
to  rush  into  the  investigation  of  a  problem  until  all  the  available 
information  on  the  subject  has  been  carefully  examined.  For  this 
reason  well-managed  colour  factories  have  a  special  department 
dealing  with  the  literature  of  the  subject  which  is  able  on  request 
to  furnish  all  details  required  from  its  carefully  compiled  indexes, 
thus  making  it  possible  to  obtain  quickly  a  complete  summary  of  the 
existing  information.  It  is  frequently  necessary  to  extend  a  given 
reaction  over  a  wide  field,  and  possibly  to  make  hundreds  of  different 
dyes  and  preparations,  as  it  is  usually  found  that  only  quite  a  few  of 
the  compounds  sought  have  any  value  (cf.  Ehrlich-Hata  "  606  "). 
If  the  Directorate,  after  consulting  with  the  various  departments, 
such  as  the  dye-house,  pharmaceutical  laboratory,  or  other  sections, . 
finds  a  new  compound  or  process  of  sufficient  interest,  it  is  usually 
put  through  on  a  somewhat  larger  scale.  This  is  carried  out  in  the 
so-called  Small-scale  Plant,  which  is  an  intermediate  link  between  the 
laboratory  and  the  works.  In  this  technical  laboratory  is  found 
apparatus  which  is  larger  than  that  used  in  the  research  laboratories, 
but  is,  of  course,  far  smaller  than  the  actual  works  plant.  In  this 
way  it  is  possible  to  get  an  idea  as  to  how  the  reaction  is  likely 
to  go  on  the  large  scale,  thus  frequently  saving  large  sums  of 
money. 

Further,  at  this  stage  it  is  decided  whether  a  reaction  or  a  com- 
pound shall  be  patented.  It  is  the  task  of  the  patent  department 
to  decide  as  to  the  likelihood  of  obtaining  a  patent  or  whether,  if  the 
discovery  appears  to  be  important,  it  would  be  preferable  to  keep 
it  secret  until  the  whole  field  has  been  investigated,  and  there  is 
little  danger  of  any  one  else  trespassing.  Very  occasionally  patent 
protection  is  not  sought,  and  the  attempt  is  made  to  keep  the 


TECHNICAL  NOTES   ON  WORKS   MANAGEMENT     213 

processes  secret,  but  this  is  by  no  means  a  safe  proceeding,  and  is 
only  resorted  to  in  cases  of  necessity. 

The  chemists  are  required  to  submit  a  report  on  their  activities 
to  the  Directorate  at  regular  intervals  in  order  that  the  Directors 
and  heads  of  departments  may  be  kept  in  touch  with  all  develop- 
ments. These  reports  are  submitted  monthly,  or  at  less  frequent, 
but  regular,  intervals,  and  are  drawn  up  under  the  supervision  of  the 
departmental  heads. 

Before  a  product  is  put  on  to  the  works  to  be  manufactured  it  is 
first  sent  to  the  Costing  Department  to  be  costed.  The  necessary 
data  are  provided  by  the  chemical  administrative  staff  and  the  works 
engineer.  In  Chapter  15  a  small  calculation  is  shown  as  an  example, 
in  order  to  give  a  general  idea  of  the  manner  in  which  the  cost-price 
of  a  dye  is  arrived  at. 

Management. — The  actual  Management  is  divided  into  three 
sections,  the  Technical  Chemical  Department,  the  Analytical  and 
Dyeing  Department,  and  the  Engineering  Department. 

Owing  to  the  destructive  action  of  the  chemicals  used,  apparatus 
is  very  quickly  worn  out  and,  in  addition,  alterations  are  frequently 
necessary,  so  that  the  ratio  of  the  number  of  chemical  workers  to 
that  of  the  ordinary  workmen  (e.g.  locksmiths,  pipe-fitters,  car- 
penters, painters,  bricklayers,  etc.)  is  about  2:1.  The  workshops 
are  first  of  all  repairing  shops,  and  are  under  the  direction  of  the 
works  engineer.  If  any  repair  or  alteration  is  required  to  an  existing 
plant,  the  works  chemist,  with  the  sanction  of  the  management 
if  it  is  a  large  matter,  applies  to  the  engineer.  The  work  is  ordered 
by  means  of  a  special  form  duly  filled  in,  which,  on  completion  of 
the  job,  is  sent  to  the  Costing  Department  to  be  worked  out. 

The  large  dye  factories  have  their  own  constructional  workshops, 
but  nevertheless  place  their  large  orders  outside  after  making  a 
suitable  agreement  with  some  engineering  works  for  quick  delivery 
at  reasonable  rates.  It  is  advisable  not  to  use  too  many  types  of 
plant  so  that  any  part  or  agitator  may  be  replaced  at  once  from  stock. 
Frequently  quite  a  few  spares  suffice  for  many  different  plants,  as 
they  are  mutually  interchangeable. 

Charges. — In  addition  to  the  charges  due  to  depreciation  and 
repairs,  there  are  maintenance  charges  of  various  kinds  to  be  con- 
sidered. Some  of  these  are  calculated  exactly,  whilst  others  are 
lumped  together  as  general  overhead  charges  or  "  On-costs."  The 
expenses  which  can  be  estimated  fairly  accurately  are  workmen's 
wages,  which  can  be  calculated  from  the  wage-sheets  of  the  foremen 
and  works  chemists  ;  further,  the  steam  consumption  can  be 


2i4  TECHNICAL  DETAILS 

measured  with  the  usual  type  of  steam  meter,  and  also  the  amount  of 
compressed  air  and  vacuum  used. 

Steam  Consumption. — The  steam  consumption  of  a  colour 
factory  is  considerable,  and  depends  upon  the  amount  of  water 
which  requires  to  be  heated  and  on  the  number  of  cubic  metres 
of  water  which  have  to  be  evaporated.  In  particular,  the  evaporation 
of  reduction  liquors  demands  immense  quantities,  and  multiple-effect 
evaporators  (double  and  triple  effect)  are  being  increasingly  used. 
In  this  type  of  apparatus  the  heat  of  the  steam  is  used  two  or  three 
times  over  by  leading  the  waste  steam  into  a  second  boiler,  where  it 
evaporates  a  further  quantity  of  liquid  kept  under  reduced  pressure. 
This  apparatus  is  modelled  partly  upon  the  multiple-effect  evaporators 
used  in  the  beet-sugar  industry,  and  in  some  cases  they  possess 
heating  vessels  which  are  placed  next  to  the  reservoir  of  liqud.  The 
liquid  is  made  to  circulate  through  the  tube  evaporator,  thus  attaining 
a  rapid  circulation,  and  in  addition  the  boiler-scale  (chiefly  gypsum) 
is  deposited  solely  in  the  subsidiary  vessel,  the  tubes  of  which  can  be 
replaced  in  a  few  hours.  It  is  possible  by  this  regenerative  utilization 
of  the  steam  to  reduce  the  coal  consumption  to  less  than  25  %,  so 
that  the  large  dye-works  use  triple-effect  evaporators  almost  ex- 
clusively with  very  satisfactory  results.  It  is  possible  to  utilize  the 
steam  still  more  efficiently  by  heating  it  up  to  15  atmospheres  instead 
of  the  usual  working  pressure  of  5  atmos.  Before  this  high-pressure 
steam  reaches  the  works  it  is  used  to  drive  a  steam  turbine  or  a 
reciprocating  engine,  leaving  this  at  5  atmos.  pressure.  So  much 
energy  is  obtainable  from  the  pressure  drop  of  15-5  atmos.  that  each 
dye  works  can  actually  provide  surplus  electric  current.  It  "has 
also  been  suggested  that  the  steam  should  be  allowed  to  fall  as  low 
as  2  atmos.,  but  in  order  to  do  this  the  steam  pipes  must  be  so  large 
and  the  radiation  losses,  particularly  in  winter,  so  considerable,  that 
it  is  hardly  practical  politics .  Of  recent  years  an  improved  method  for 
using  up  steam  has  been  introduced,  although  the  general  principle 
has  been  known  for  a  long  time.  The  liquid  under  evaporation  is 
placed  in  an  hermetically  closed  evaporator,  the  vapours  are  sucked 
out  by  means  of  a  turbo-blower,  and  the  waste  steam  is  then  circu- 
lated, under  a  pressure  of  about  f  atmos.  through  a  system  of  tubes 
built  into  the  same  vessel.  There  is  a  considerable  evolution  of 
heat  as  a  result  of  the  compression  of  the  vapours,  so  that  as  much  as 
80  %  of  fuel  may  be  saved.  Apparatus  of  this  type  is  becoming 
increasingly  popular,  and  is  made,  for  example,  by  Gebr.  Sulzer  in 
Winterthur,  and  by  Escher  Wyss  in  Zurich. 

Compressed  Air  and  Vacuum, — In  addition  to  steam,  the 


PLATE   XVIII. 


TECHNICAL  NOTES   ON  WORKS   MANAGEMENT     215 

provision  of  compressed  air  is  also  important.  Generally  a  pressure 
of  2-3  atmos.  is  needed,  which  is  obtained  by  the  use  either  of  a 
reciprocating  or  a  rotating  pump.  The  chief  determining  factor  as 
to  the  quantity  of  air  required  is  the  number  of  filter-presses,  as 
these  use  the  most  air.  Every  precipitate  before  leaving  the  press 
is  "  blown  through  "  for  a  time,  i.e.  compressed  air  is  blown  through 
the  filter-cakes  until  the  main  portion  of  the  mother-liquor  has  been 
blown  out.  For  instance,  a  press  with  40  sections  will  require  about 
100  cubic  metres  per  hour  of  compressed  air  at  2  atmos.,  which  will 
cost  from  3-5  centimes,  according  to  the  price  of  the  current. 

The  provision  of  air  for  a  dye  works  is  therefore  a  considerable 
item  of  expenditure,  and  must  be  carefully  estimated.  A  very 
satisfactory  type  of  compressor  and  vacuum  pump  is  that  shown  on 
Plate  XVI,  made  by  the  Schweiz  Lokomotiv  und  Maschinenfabrik 
in  Winterthur  (Witte's  system,  cf.  also,  p.  189). 

The  cost  of  the  water  used  must  also  be  carefully  determined  by 
the  engineer  by  accurate  measurement,  as  very  large  quantities  of 
water  are  employed,  particularly  as  cooling  water  for  the  condensers. 

Duties  of  the  Works  Chemist. — The  work  of  the  supervising 
chemist  is  possibly  the  most  interesting  in  the  whole  of  the  industry, 
as  it  is  impossible  to  control  chemical  reactions  merely  by  giving  an 
order,  but  their  course  must  be  accurately  followed  the  whole  time 
and  any  deviations  corrected.  The  chemist  must  be  au  courant  with 
the  whole  process,  and  must  know  every  stage  of  the  manufacture  in 
full  detail.  In  this  connection  attention  may  be  called  to  the  remarks 
made  on  Benzo  Fast  Blue  (pp.  144—5). 

Manufacture. — The  ordering  of  the  necessary  raw  products  is 
done  by  means  of  requisition  forms  which  are  usually  sent  to  the 
Material  Stores  on  the  previous  day,  or  occasionally  to  some  other 
department  of  the  works.  The  chemicals  are  brought  to  the  shed 
on  the  evening  before  they  are  required  so  that  everything  will  be 
ready  when  the  manufacture  is  begun.  The  chemist  is  responsible 
for  the  products  until  the  moment  that  they  issue  in  the  dry  form 
from  the  shed.  As  many  colours  are  sensitive  to  heat,  and  therefore 
require  careful  heating,  their  drying  must  always  be  supervised  by 
the  chemist  so  that  he  will  always  be  able  to  give  an  account  of  the 
effect  of  the  drying  upon  the  strength  and  shade  of  a  dye.  Such 
cases  have  been  dealt  with  in  connection  with  Methylene  Green  and 
Azo  Yellow. 

Standard  Dye- House. — The  finished  colour  is  sent  directly 
from  the  drying  shed  to  the  dye-house,  where  a  small  sample  is  dyed 
out  against  the  Type  or  Standard.  The  figures  obtained  are  sent 


216  TECHNICAL   DETAILS 

immediately  to  the  management,  the  costing  department,  and  the 
chemist  concerned  in  the  matter,  so  that  all  may  be  kept  con- 
tinuously informed.  Frequently  a  dyeing  test  is  carried  out  with 
a  small  sample  of  the  colour  taken  directly  from  the  filter-press,  so 
that  any  faults  may  be  recognized  at  that  stage. 

Drying. — In  recent  years  vacuum  drying  chests  have  been  coming 
more  and  more  into  use,  as  it  has  been  shown  that  the  steam  con- 
sumption is  less  and  the  strength  of  the  product  greater.  Plate  XVI 
shows  a  modern  vacuum  dryer  as  used  with  various  modifications. 
Stable  intermediate  products  such  as  sodium  /3-naphthalene  sul- 
phonate,  and  simple  azo  colours,  can  be  dried  simply  on  steam 
plates,  or  may  even  be  dehydrated  in  tunnel-kilns  on  the  counter 
current  system,  though  here  also  vacuum  drying  is  becoming  more 
general  owing  to  the  saving  both  of  time  and  space.  The  Badische 
Anilin-  und  Sodafabrik,  for  instance,  make  use  of  about  500  vacuum 
dryers,  and  have,  so  far  as  possible,  given  up  the  older  system  of 
drying. 

In  order  to  dry  a  product  rapidly  it  must  be  ground  up  at  least 
once  during  the  drying.  As  much  dust  is  formed  during  this  breaking 
up  of  the  press-cake,  many  drying  sheds  are  provided  with  dust 
extractors. 

A  modern  improvement  is  to  condense  the  vapours  from  the 
drying  chests  so  that  the  pumps  do  not  suffer  so  much  from  the 
action  of  acid  or  alkaline  vapours. 

Standardization. — When  a  certain  number  of  works  batches 
have  been  dried,  they  are  ground  up  and  made  up  to  a  standard  or 
type  strength.  The  grinding  and  mixing  is  usually  carried  out  in  a 
special  mixing  department  which  is  under  the  control  of  the  dye- 
house.  (This  dye-house  has  no  connection  with  the  scientific  and 
commercial  propaganda  dye-house,  which  is  intended  to  serve  quite 
another  purpose.) 

Grinding. — Nowadays  the  colours  are  ground  up  in  modern 
centrifugal  mills,  such  as  that  shown  diagrammatically  on  Plate  XVII. 
The  capacity  of  such  a  machine  exceeds  that  of  the  older  edge- 
runner  mill  or  ball-mill  by  some  10-50  times,  whilst  at  the  same 
time  the  particles  are  ground  smaller.  Many  complaints  of  in- 
adequate solubility  of  a  product  are  to  be  ascribed  to  incorrect 
grinding,  as,  in  the  older  types  of  apparatus,  the  substances  were 
pressed  together,  thus  producing  almost  shaly  tablets  of  great  hard- 
ness which  dissolve  only  with  difficulty. 

Whenever  possible  the  approximate  necessary  quantity  of  diluent 
is  ground  up  with  the  dye  so  as  to  diminish  the  length"  of  time 


TECHNICAL  NOTES  ON  WORKS   MANAGEMENT     217 

necessary  for  the  mixing.  The  concentrated  colour  is  mixed  with 
the  standardizing  material  (Glauber  salt,  common  salt,  soda,  or 
dextrin),  and  the  mixture  is  run  into  the  mill.  The  disintegrator 
illustrated  has  an  automatic  sieve  and  also  magnets  for  the  removal 


FIG.  39. — Diagram  of  a   "  Perplex  "   disintegrator. 

B.  Feed-pipe,     i.  Fixed   grinding  pins.     2.  Rotating  pins  (1200-2000  rotations 

per  minute).     3.  Sieve. 

of  iron  particles,  which  are  always  present  in  the  materials.  The 
dye  is  broken  up  whilst  in  motion  by  the  specially  shaped  grinding 
pins,  and  is  whirled  round  and  round  until  it  passes  through  the 
sieve  (Fig.  39).  Owing  to  the  centrifugal  effect,  much  air  is  sucked  in, 


2i 8  TECHNICAL   DETAILS 

which  must  be  allowed  to  pass  out  from  the  apparatus  again.  Filter- 
bags  (G,  Plate  XVII)  in  the  form  of  piping  permit  the  escape  of  the 
air,  but  keep  back  all  the  dust.  The  main  portion  of  the  powder  is 
retained  in  the  air  chamber  (F),  the  stream  of  air  striking  the  walls 
tangentially.  If  very  soft  material  is  being  disintegrated,  such  as 
^8-naphthol  or  naphthalene,  it  is  better  not  to  have  the  sieve  as  it  is 
readily  stopped  up.  The  ground  products  are  carried  by  means  of 
worm-conveyors  direct  into  the  mixing  troughs,  where  they  are  well 
mixed  up  for  several  hours.  Plate  XVII  (Fig.  42)  shows  a  modern 
mixer  which  can  be  filled  or  emptied  automatically  by  means  of  a  re- 
versible worm-feed.  This  type  of  mixing  apparatus  is  made  for  deal- 
ing with  quantities  up  to  4  tons,  and  is  gradually  replacing  the  older, 
uneconomical  mixers,  particularly  when  very  large  quantities  are 
being  dealt  with.  Simpler  mixers  are  also  made  use  of  which  are 
provided  with  compressed  air  and  vacuum,  like  grain-silos.  Certain 
dyes  must  be  pulverized  outside  the  grinding  shed  owing  either  to  a 
danger  of  fire  (picramic  acid  dyes)  or  owing  to  their  unpleasant 
properties  (e.g.  Bengal  Blue  or  Naphthol  Blue,  p.  173).  As  soon  as 
the  strength  and  shade  has  been  passed  by  the  dye-house  as  correct, 
the  dye  is  sent  off  to  the  packing-house,  from  whence  it  is  handed 
over  to  the  Sales  Department.  The  management,  costing  depart- 
ment, and  works  chemist  are  all  informed  of  any  matters  of  special 
interest  such  as  good  or  bad  yields  or  shades.  The  responsibility  of 
the  works  chemist  finishes  with  the  delivery  of  his  products  whether 
dyes  or  intermediates. 


15.   EXAMPLE   OF  THE   COSTING   OF  A   SIMPLE  DYE  l 

Orange  II  =  Acid  Orange  A. 
(Sulphanilic  Acid — /3-Naphthol ;  see  p.  113.) 

The  costing  of  the  product  of  the  dye  factory  is  always  done  by 
the  Costing  Department.  This  department  obtains  daily,  weekly, 
or  monthly,  the  necessary  data  from  the  various  manufacturing 
departments,  from  which  the  prices  may  be  calculated  with  very 
great  accuracy.  The  position  of  head  of  the  Costing  Department  is  a 
very  responsible  one,  and,  next  to  the  actual  management,  he  is  the 
most  important  person  in  a  modern  colour  factory. 

1  The  prices  and  charges  used  in  this  calculation  represent  average  figures  for 
1913  14.  The  example  is  intended  simply  to  show  the  beginner  how  the  final  cost 
of  a  relatively  simple  Azo  dye  is  made  up  from  numerous  separate  items. 


EXAMPLE  OF  THE   COSTING   OF  A  SIMPLE  DYE    219 

The  cost  of  a  product  is  made  up  solely  from  the  cost  of 
materials  and  the  workmen's  wages. 

Every  item  which  is  to  be  added  to  the  price  of  a  product  must  be 
based  upon  very  carefully  scrutinized  figures. 

We  will  first  determine  the  cost  of  the  separate  components. 


Fr. 

260  kgs.  Naphthalene  at  n  frs.  per  100  kilos.      .          .  .  28*60 

280  kgs.  Sulphuric  acid  at  2*70  frs.  per  100  kilos.          .          .  7*56 

60  kgs.  Soda  at  9  frs.  per  100  kilos.  .          . 

60  kgs.  Coal  at  2  frs.  per  100  kilos.  .          .          . 

350  kgs.  Salt  at  1*40  frs.  per  100  kilos.        .       •.  » 

Yield  of  /^-naphthalene  sulphonate  165  %  =429  kgs.—          .          .    47*66 
.*.  100  kgs.  cost  11*10  frs. 

This  price  is  known  as  the  "  First  Price"  or  "  A  price"  It 
contains  only  the  cost  of  the  materials  purchased  or  obtained 
from  other  departments  (for  instance,  sulphuric  acid  from  the  acid 
factory,  etc.). 

There  are  a  number  of  other  charges  to  be  added  to  this  First 
Price,  which  are  made  up  from  items  such  as  wages,  repair,  or  wear 
and  tear  of  apparatus,  cloths  for  pressing  filter-cakes,  drying  of  the 
sulphonate,  cost  of  carriage,  grinding,  power,  steam,  and  water. 
All  these  figures  must  be  very  accurately  determined  if  a  correct 
idea  of  the  whole  process  is  to  be  obtained.  It  is  hardly  necessary 
to  add  that  these  calculations  can  only  be  carried  out  by  a  carefully 
trained  staff.  The  calculation  of  the  workmen's  wages  is  based  upon 
the  time-sheets,  which  are  controlled  and  examined  by  the  super- 
intendent. 

The  works  chemist  should  be  concerned  as  little  as  possible 
with  administrative  duties  of  this  kind  as  they  merely  keep  him  from 
his  real  business,  namely,  chemistry.  He  should  keep  an  eye, 
however,  upon  the  works  log  book  and  the  chemical  log  book  at 
least  each  week,  the  resultant  figures  only  going  to  the  Costing  Depart- 
ment when  he  has  passed  them. 

In  a  similar  manner  the  other  charges  are  obtained  from  those 
in  charge  of  the  stores  and  the  repairing  shops,  and  from  the  data 
furnished  by  the  works  engineer.  It  is  usual  to  carry  out  tests  from 
time  to  time,  by  actual  measurements,  of  the  steam  and  water 
requirements  for  a  given  product. 

These  charges  may  be  spread  over  the  different  products  in 
various  ways.  For  the  sake  of  simplicity  we  will  assume  that  the 

1  Based  on  the  assumption  that  the  factory  is  in  a  country  producing  its  own 
coal. 


220  TECHNICAL  DETAILS 

charges  are  in  respect  of  100  kilos,  of  dried  product,  and  that  it  has 
been  determined  that  the  various  charges  for  the  dry  /3-naphthalene 
sodium  sulphonate  are  calculated  as  follows  : — 

Fr. 

Wages,  2  hours  at  o'8o  frs.  per  100  kilos,  (including  insurance,  wel- 
fare, etc.)  .  .  .  .  .  .  .  .  .  .  .  i'6o 

Power,  4  k.w.-hours  at  4  centimes  per  k.w.-hour  (pressing  and 

stirring,  including  compressed  air)  •  .  .  .  .  0*16 

Drying  and  grinding  at  20  centimes  per  100  kgs.  (tunnel-kiln 

drying)  .  .  .  .  .  .  .  .  0*20* 

Total  charges  for  producing  100  kilos.  sodium-/?-naphthalene 

sulphonate  .          .          .          .          ..'         .          .'..'•    1*96 

100  kilos,  (first  cost)  .  .  '  '    .         ..          .          .11*10 


13*06 


Alkali  Melt  of  Sodium  Salt. 


In  actual  practice  large  amounts  (from  400  to  2000  kilos,  of  the 
sodium  salt)  are  melted,  but  to  simplify  the  calculation  we  will  assume 
that  we  are  dealing  with  a  charge  of  only  100  kilos. 

Fr. 
ioo  kgs.  "  Naphthalene  salt "  .  .          .    13*06 


45  kgs.  NaOH  at  17  frs.  per  ioo  kilos.      . 

15  kgs.  Coal  at  2  frs.  per  ioo  kilos.  . 

20  kgs.  Sulphuric  acid  at  2*70  frs.    . 
Labour  for  melting,  dissolving,  and  distilling 
Fuel  for  melt  and  distillation,  condensing  water 


air 


Interest  (5  frs.  per  ioo  kilos.,  yield  45  kgs.) 


and 


compressed 


7-65 
o'30 

°'54 
5*00 

2*00 
2-25 


Total 30-80 

Less  value  of  recovered  sulphite  and  Glauber  salt        .      2*00 

Cost  of  production  of  45  kilos,  pure  Naphthol    .          .    28' 80 
i  kilogram  pure  naphthol,  therefore,  costs  64  centimes. 

In  addition  there  are  the  general  "  on-costs  "  which  may  be 
reckoned  at  about  5  %,  so  that  the  final  cost  price  of  the  beta- 
Naphthol  is  about 

67  centimes  per  kilogram. 

In  Switzerland  it  is,  of  course,  quite  impossible  to  get  such  low 
figures,  as  coal  and  other  raw  materials  are  far  more  expensive,  so 
that  allowance  must  be  made  for  at  least  double  the  above  figure. 

Actually,  before  the  war,  ^8-naphthol  was  obtainable  in  Switzer- 
land in  barrels,  at  a  price  of  about  95  centimes  per  kilo.,  including 
packing,  freight,  and  duty.  It  may  be  seen,  therefore,  that  at  best 

1  The  drying  is  effected  by  means  of  the  waste  heat  from  the  fusion  pot. 


EXAMPLE  OF  THE  COSTING  OF  A  SIMPLE  DYE    221 

only  about  10  centimes  profit  could  be  made  per  kilo.  We  can 
therefore  put  our  naphthol  at  about  95  cts.,  with  the  proviso  that 
the  large  German  works  had  a  lower  cost-price  as  they  were  able  either 
to  make  large  contracts  on  favourable  terms  or  to  manufacture  the 
naphthol  themselves.  In  any  case  the  manufacture  shows  so  little 
profit  that  the  majority  of  factories  prefer  to  purchase  their  naphthol 
from  the  large  works  who  do  make  it,  and  to  concern  themselves 
with  more  profitable  products. 


Sulphanilic  Acid. 

(a)  Nitrobenzene  : 

FT. 
i oo  kgs.  Benzene  at  32  cts.        .          .          .          ...          .          .    32*00 

no  kgs.  HNO3  (75  %)  at  40  cts,       .          .  .         ..    44*00 

170  kgs.  K2SO4  2*70  frs.  .          .          .          ...          .      4*60 

80*60 

Yield  :    154  kgs. 

Repairs  and  depreciation,  50  cts.  per  100  kgs.     .          .          .          .0*77 
Labour,  at  35  cts.  per  100  kgs.  ...          .          .          .          .      0*54 

Total  for  154  kgs.  Nitrobenzene       .          .          .          .          .81*91 
Less  3  frs.  for  recovered  spent  acid  ....    78*91 

Cost  of  i  kilo.  Nitrobenzene  about  55  centimes. 

Actually  the  larger  works  can  produce  it  more  cheaply,  at  less 
than  50  centimes. 

(b)  Reduction  of  Nitrobenzene  : 

We  will  assume  that  exactly  the  154  kgs.  are  reduced,  remembering, 
however,  that  in  actual  practice  charges  up  to  2000  kgs.  are  dealt  with. 

Fr. 
Nitrobenzene,  154  kgs.  about   ......  85*00 


Iron,  40  kgs.  at  3  cts. 
Hydrochloric  acid,  4  kgs.  at  4  cts. 
Lime,  4  kgs.  at  1*25  frs.  per  100  k 


1*20 
0*16 
0*05 


juime,  4  Kgs.  at  1*25  Irs.  per  100  kgs.  .... 

Steam,  repairs,  depreciation,  distillation,  power,  etc.,  for  154  k_ 

Nitrobenzene       .          .          .          .          .          .          .          .  5*00 

Total      ..........    91*41 

Yield  no  kgs.     Price  per  kilo.  83*1  centimes. 

If  it  is  remembered  that  the  price  of  aniline  has  at  times  gone  down 
as  low  as  85  cts.  per  kilo,  in  the  open  market,  it  is  not  difficult  to 
realize  that  practically  no  profit  could  have  been  obtained  on  it,  and 
the  suggestion  sometimes  made  by  purchasers  that  too  high  prices 
were  charged  for  it  is  seen  to  be  without  foundation.  At  the  same 
time  it  is  certain  that  the  large  aniline  works,  such  as  Weiler-ter-Meer 
and  others,  had  considerably  lower  production  costs. 


222 


TECHNICAL   DETAILS 


no  kgs.  Sulphuric  acid  at  2*70  frs.    .          .          .          , 
93  kgs.  Aniline  at  i  fr.  per  kg.  (price  in  Switzerland) 


Fr. 


.     93-00 

95'97 
4'  oo 
.       2-50 
.      0-17 

.  102*64 


Labour,  5  hours  at  80  cts.         .          .."•'»• 
Steam  (baking-stove)  coal          .          .          ... 
Upkeep  at  10  cts.  per  100  kgs.  .          ... 

Total        .          .          .  .          .          . 

Yield  about  163  kgs.  100  %  Sulphanilic  acid. 
Price  about  70  cts.  per  kilo. 

We  have  now  determined  approximately  the  prices  of  the  inter- 
mediate products,  but  these  will,  of  course,  vary  according  to  circum- 
stances and  serve  chiefly  to  show  how  difficult  it  is  to  get  really 
accurate  figures. 

We  will  assume  that  the  Sulphanilic  acid  costs  us  70  cts.,  and  the 
/3-naphthol  95  cts.  per  kilo.,  according  to  the  usual  conditions 
obtaining  in  Switzerland. 


Preparation  of  the  Dye  from  Sulphanilic  Acid  and 
/3-Naphthol. 

We  will  take  the  kilogram-molecule  for  our  unit,  and  for  this 
purpose  we  multiply  up  the  Acid  Orange  charge  given  on  p.  113  by 
10,000. 

Fr. 

173  kgs.  Sulphanilic  acid  at  70  cts.  per  kg.                     .  .  i2i'io 

60  kgs.  Sodium  carbonate  at  7  cts.  (Swiss  price    10  cts.)  .      4*20 

144  kgs.  ^-Naphthol  at  95  cts.  per  kg.         .  .         .  i36'8o 

144  kgs.  Caustic  soda  lye  (30°  Be.)  at  6  frs.  per  100  kg  '         .       8*64 

no  kgs.  Sulphuric  acid  at  2*70  frs.  (Swiss  4*0)  '         .      2'97 

70  kgs.  Sodium  nitrite  at  51  frs.  per  100  kg.  .          .    35*70 

250  kgs.  Sodium  carbonate  at  7  cts.  per  kg.  .          .     17*50 

800  kgs.  Ice  at  80  cts.  per  100  kgs.     .  .      6*40 

200  kgs.  Salt  at  1*40  frs.  (Swiss,  about  3*50)  .      2*80 

Total 336*11 

Yield  about  400  kgs.  concentrated  product;  containing 
salt  and  soda  as  impurities. 

Labour,  12  hours  at  80  cts.       .          .          . 

Running      expenses     based     on     dry     concentrated      product 
per  100  kgs. : — 

Drying  400  kgs.  at  8  frs.  per  100  kgs. 

Mixing  and  grinding,  at  4  frs.  per  100  kgs. 

Air,  steam,  water,  power,  at  4  frs.  per  100  kgs.       . 

Total  .      '•...' 


Fr. 
9' 60 


32*00 
i6'oo 
1 6*00 

73-60 


The  dye-house  expenses  are  either  charged  up  to  the  process 
or  to  the  general  account.     In  the  opinion  of  the  author  only  the 


EXAMPLE  OF  THE  COSTING   OF  A   SIMPLE  DYE    223 

expenses  of  the  standardizing  dye-house  should  be  included,  the  cost 
of  the  upkeep  of  the  "  propaganda  "  dye-house  being  allocated  to 
the  general  propaganda  and  advertising  account.  These  latter 
expenses  are  much  larger  than  those  for  the  standardizing  dye-house, 
and  logically  they  should  be  kept  as  separate  items. 

We  include  here,  therefore,  only  the  manufacturing  charges, 
which  we  may  estimate  at  about  1*80  francs  per  100  kgs.  of  finished 
product,  which  equals  7*20  frs.  : 

Fr. 

Dye-house  charges  .          .          .          .         '/.'',-       .          .      7' 20 

Other  charges         .          .          .          .          .          .          .          .          .     73*60 

Total  of  "  On  costs,"  excluding  general  works  expenses      .    8o'8o 
Total  first  costs  of  Acid  Orange  A,  excluding  general  works 

charges,  for  400  kgs.  .....          .336*11 

Total        .        '.         ..          .          .          .          .          .          .  416*91 


In  addition  there  must  be  added  certain  other  charges,  usually 
termed  general  works  expenses,  which  are  made  up  from  the  following 
items  :  railway,  cleaners,  etc.,  stores,  care  of  the  factory  (porter, 
night-watchman,  etc.).  The  costs  of  the  analytical  and  works 
laboratories  are  also  included,  but  not  the  salaries  of  the  research 
chemists. 

This  figure  may  vary  very  considerably  according  to  the  amount 
of  the  turnover.  Usually  these  general  expenses  may  be  estimated 
at  about  5-7  %  of  the  value  of  the  finished  dye.  Occasionally  with 
products  which  are  meeting  with  keen  competition,  smaller  expenses 
will  be  charged  up  to  them,  but  such  matters  are,  of  course,  essentially 
for  the  Sales  Department,  and  are  decided  by  the  managerial  staff. 

In  the  present  case,  therefore,  we  may  assume  that  a  figure  of 
6  %  may  be  taken  to  cover  these  general  on-costs,  6  %  of  416*91  frs. 
=  25*02  frs.,  so  that  the  actual  cost  price  of  the  pure  product  is  441*93 
frs.  per  400  kilos. ,  or  about  no  franc  per  kilo.  This  product  is 
then  reduced  to  standard  strength  by  means  of  salt  as  mentioned 
on  p.  216. 


IV.  ANALYTICAL   SECTION 

16.   ANALYTICAL   DETAILS 

THE  exact  determination  of  the  composition  and  degree  of  purity 
of  the  raw  and  intermediate  materials  used  for  the  production  of  dyes 
is  of  the  greatest  importance.  The  methods  in  use  are  partly  physical 
and  partly  chemical.  In  many  cases  it  suffices  to  obtain  certain 
physical  data  such  as  Melting  Point,  Solidifying  Point,  and  Boiling 
Point ;  aniline,  the  toluidines,  nitro  compounds,  etc.,  are  usually 
tested  in  this  way.  Sometimes  the  Specific  Gravity  (Density)  is 
determined  in  addition,  and  occasionally  also  the  Refractive  Index 
for  monochromatic  light.  Practically  all  the  important  details  are 
given  in  Lunge's  work  on  "  Coal  Tar  and  Ammonia."  The  properties 
required  are  often  specified  in  the  contract,  and  serve  as  standard 
to  work  by  in  case  of  any  differences  being  detected. 

At  the  present  day  intermediates  are  placed  on  the  market  in 
such  a  pure  form  that  all  reasonable  requirements  can  be  fulfilled. 

Samples  of  materials  which  it  is  proposed  to  purchase  should  in 
all  cases  be  tested  in  the  Analytical  Laboratory  ;  the  method  of 
sampling  is  frequently  specified  in  the  contract.  Even  the  method 
of  heating  to  be  adopted  when  determining  the  melting  or  solidifying 
points  is  usually  standardized.  In  the  works  the  practice  is  some- 
times adopted  of  determining  the  strength  of  the  technical  solutions 
in  use,  the  actual  yield  being  only  estimated  at  the  end  of  the  process. 
In  the  larger  factories,  however,  it  is  becoming  increasingly  the  custom 
to  weigh  all  solutions  at  once  in  their  barrels,  scales  being  used  which 
can  weigh  up  to  40,000  kgs.  with  a  sensitiveness  of  100  gms. 

Each  product  used  in  the  dye  industry  is  characterized  by  its 
Molecular  Weight,  which  is  calculated  simply  from  its  chemical 
formula.  Owing  to  the  fact  that  various  substances  are  used  in 
different  forms,  e.g.  benzidine  as  sulphate  and  as  base,  Cleve  acid  as 
free  acid  and  as  the  sodium  salt,  it  is  customary  to  give  one  molecular 
weight  to  each  given  substance,  the  salt  being  reckoned  as  of  a  corre- 
spondingly lower  degree  of  purity.  When  purchasing  materials, 
therefore,  it  is  necessary  to  ascertain  the  molecular  weight  of  the 

224 


PLATE  XIX. 


FIG.  45. — Screw  press  with  wrought  iron  frame  (made  by  Preiswerk  and  Esser, 
Basle).  The  base-plate  is  covered  with  copper  sheet  and  the  products  are 
pressed  between  hard-wood  boards. 


ANALYTICAL   SECTION  225 

bodies  as  well  as  the  price  per  kilo.  Suppose,  for  instance,  that 
i  kg.  benzidine  (mol.  wt.  =  184)  costs  3  frs.  per  kilo.,  and  i  kg. 
benzidine  sulphate  (mol.  wt.  =  282)  2  frs.  per  kilo.,  then  the  pure  base 
in  the  sulphate  will  cost  2X282/184  =  3*02  frs.,  that  is  to  say,  the 
price  is  practically  identical.  This  is  sometimes  expressed  by  giving 
the  degree  of  purity  as  a  percentage.  In  the  present  case,  for  instance, 
the  sulphate  would  be  65-2  %  (mol.  wt.  =  i84),  i.e.  184  kgs.  benzidine 
base  (mol.  wt.=i84)  will  be  obtained  from  282  kgs.  sulphate. 


Preparation  of  Standard. 

Sodium  nitrite  is  generally  estimated  in  commerce  by  oxidation 
with  permanganate  in  the  usual  manner,  but  this  gives  values  which 
are  slightly  too  high  for  the  works  chemist.  Besides  the  nitrous  acid 
the  permanganate  gives  also  any  other  oxidizable  substances  which 
may  be  present,  so  that,  under  certain  conditions,  slight  errors  may  be 
caused.  In  spite  of  this,  however,  this  method  is  adopted  in  various 
factories,  such  as  the  Notodden  nitrite  works.  For  the  colour 
chemist,  however,  there  is  only  one  really  dependable  method, 
namely,  the  Sulphanilic  Acid  Method,  which  is  fully  as  accurate 
with  a  little  practice  and  is  safer. 

Preparation  of  pure  Sulphanilic  Acid. 

250  Gms.  of  commercial  Sulphanilic  acid  are  dissolved  in  sufficient 
sodium  carbonate  to  give  a  strongly  alkaline  solution,  which  is  boiled 
until  all  aniline  has  disappeared.  The  volume  is  about  i  litre. 
The  solution  is  now  filtered  and  made  strongly  acid  by  means  of 
hydrochloric  acid.  After  standing  12  hours  the  product  is  filtered 
off,  washed  with  a  little  water,  and  the  crystals  dissolved  to  a  neutral 
solution  in  400  c.cs.  water  and  a  sufficient  quantity  of  soda  (about 
60  gms.)  The  hot  solution  is  cooled  down  to  o°  with  continuous 
stirring  and  the  sodium  sulphanilate  is  filtered  off.  If  a  small 
centrifuge  is  available,  the  mother-liquor  is  "  whizzed  "  off.  The 
crystals  are  dissolved  in  500  c.cs.  of  distilled  water,  the  solution 
filtered,  and  then  acidified  with  pure  concentrated  hydrochloric  acid. 
The  liquid  is  kept  well  stirred  during  the  addition  in  order  to  ensure 
the  formation  of  small  crystals  ;  next  day  the  precipitate  is  filtered  off 
and  is  then  washed  with  a  little  distilled  water  until  the  sodium 
chloride  is  removed.  The  purified  crystals  are  again  recrystallized 
from  boiling  distilled  water  and  are  then  dried  in  an  air  oven  at  120° 
until  of  constant  weight.  The  product  is  kept  in  a  bottle  having  a 

15 


226  ANALYTICAL   SECTION 

well-fitting  ground  stopper.  The  sulphanilic  acid  so  obtained  is 
practically  white  and  contains  less  than  0*01  %  of  impurities. 
Exactly  173  gms.  are  dissolved  in  100  c.cs.  pure  ammonia  (20  %  NH3), 
and  it  is  then  made  up  to  i  litre  at  17*5°.  Such  a  solution  will 
remain  unchanged  in  the  dark  for  many  months,  but  should  be 
carefully  recontrolled  at  intervals  of  3  months. 

This  standard  solution  serves  for  the  preparation  of  Normal 
sodium  nitrite  solution. 


Preparation  of  Normal  Nitrite  Solution  (N.NaNO2). 

75  Gms.  commercial  sodium  nitrite  are  dissolved  in  a  little  water, 
filtered,  and  made  up  to  I  litre  at  17*5°.  50  C.cs.  of  the  normal 
sulphanilic  acid  solution  are  then  titrated  with  it  in  the  following 
manner  : 

The  solution  is  measured  out  into  a  half-litre  beaker  by  means  of  a 
pipette,  and  is  then  diluted  with  200  c.cs.  ice  water  and  acidified 
with  25  c.cs.  crude  cone,  hydrochloric  acid.  The  nitrite  solution  is 
then  run  in  under  the  surface  of  the  liquid  from  a  burette,  and  as 
soon  as  45  c.cs.  have  been  added,  the  remainder  is  run  in  drop  by 
drop  until  the  starch-iodide  paper  when  touched  with  a  drop  of  the 
liquid  (not  rubbed  across)  causes  a  faint  but  permanent  blue  colora- 
tion. The  diazotization  occupies  10  minutes.  From  the  number 
of  c.cs.  of  nitrite  solution  used  up  it  is  easy  to  calculate  how  much 
water  must  be  added  to  render  the  solution  exactly  normal.  It  is 
then  made  up  exactly  to  the  requisite  strength,  as  the  use  of  a  factor 
causes  too  much  unnecessary  labour.  The  little  extra  work  involved 
in  standardizing  the  solution  is  more  than  made  up  by  the  subsequent 
saving  in  time. 

When  the  sulphanilic  and  nitrite  solutions  have  been  made  up  as 
described,  a  Normal  aniline  solution  is  also  prepared  :  200  c.cs.  pure 
aniline  are  distilled  from  a  small  distilling  flask  as  shown  in  Fig^  43 1 
at  such  a  rate  that  the  distillation  occupies  about  three-quarters  of  an 
hour.  The  fraction  of  aniline  distilling  within  half  a  degree  and 
between  184  and  185°  is  used  for  the  preparation  of  the  solution. 
In  passing  it  may  be  noted  that  almost  chemically  pure  aniline  is 
obtainable  commercially.  The  specific  gravity  should  be  between 
1*0260-1*0265  at  17*5°. 

Exactly  93  gms.  pure  aniline  are  dissolved  in  150  c.cs.  of  pure 

1  High-boiling  liquids  are  generally  distilled  with  this  simple  type  of  apparatus 
i.e.  without  the  use  of  a  Liebig  condenser,  the  receiver  being  sometimes  cooled 
with  a  stream  of  water. 


ANALYTICAL  SECTION  227 

30  %  hydrochloric  acid,  and  the  solution  is  made  up  to  i  litre  at 

If  the  sodium  nitrite  solution  and  the  sulphanilic  acid  solution 
have  been  correctly  prepared  100  c.cs.  sulphanilic  acid  solution  and 
100  c.cs.  aniline  solution  should  each  require  exactly  100  c.cs.  nitrite. 

Preparation  of  N/io  Phenyldiazonium  solution. 

50  C.cs.  of  aniline  solution  are  measured  out,  treated  with 
50  c.cs.  concentrated  hydrochloric  acid,  and  the  mixture  cooled  by 
standing  the  measuring  flask  in  ice  water.  50  C.cs.  N-nitrite  solution 
are  then  added  to  it  with  gentle  shaking,  and  the  whole  allowed  to 


FIG.  43. — Distillation  of  a  liquid  of  high  boiling-point. 

stand  in  ice  water  for  20  minutes.  At  the  end  of  this  time  all  the 
nitrous  acid  will  have  been  used  up  except  for  the  merest  trace,  and 
the  solution  is  then  made  up  to  500  c.cs.  and  is  ready  for  use.  Not 
less  than  20  minutes  must  be  allowed  to  elapse  before  using  the  solu- 
tion as  the  diazotization  under  these  circumstances  takes  some  time. 
Such  a  solution  will  keep  in  the  dark  at  o°  for  about  4  hours,  and  must 
always  be  freshly  made  for  use. 


Estimation  of  Amines. 

(a)  Direct  Estimation. 

The  method  consists  in  titrating  the  amine  in  very  dilute  solution 
with  hydrochloric  acid  and  sodium  nitrite,  the  resultant  diazonium 


228  ANALYTICAL  SECTION 

solution  being  then  coupled  up  with  an  exactly  determined  amount  of 
a  phenol,  usually  Schaffer  salt,  the  diazotization  being  thus  con- 
trolled. In  the  cases  of  H-acid,  Amido-R-salt,  etc.,  one  portion  is 
diazotized  whilst  another  sample  is  coupled  up  with  aniline  or  other 
component.  Sometimes  it  is  possible  to  estimate  two  substances 
in  the  presence  of  one  another  if  one  reacts  much  more  rapidly  than 
the  other.  For  instance,  with  a  little  practice  it  is  quite  possible  to 
estimate  G-salt  and  R-salt  side  by  side  with  a  fair  degree  of  accuracy, 
as  R-salt  couples  very  rapidly  and  gives  a  red  dye  with  aniline,  whilst 
G-salt  couples  afterwards  and  forms  a  yellow  dye.  In  addition  to 
these  methods  there  are  a  number  of  special  methods  which  make  it 
possible  to  estimate  the  various  components  in  a  mixture.  Such 
methods  have  been  noticed  when  discussing  mixtures  of  R-  and 
G-salts  (cf.  p.  233). 

Certain  other  diazo  components  are  used  occasionally  in  place  of 
benzene  diazonium  chloride  ;  thus,  many  works  prefer  to  use 
w-xylidine  in  place  of  aniline,  but  there  is  very  little  point  in  so  doing, 
as  its  solution  is  less  stable  than  the  aniline  solution.  Again,  in  some 
cases  />-aminoacetanilide  is  made  use  of  as  it  couples  up  rather  more 
energetically  and  is  quite  reasonably  stable  (vide  Chromotrope  acid)  ; 
ortho-  and  para-nitranilines  are  rarely  used. 

5  Gms.  sodium  carbonate  are  required  for  each  gm.  nitrite  or,  if 
the  coupling  is  carried  out  in  acetic  acid  solution,  at  least  15  gms. 
sodium  acetate  are  added,  or  twice  this  amount  in  the  case  of  the 
nitranilines.  Should  the  substances  contain  sulphonic  groups,  still 
more  sodium  carbonate  or  acetate  will  be  required.  The  temperature 
for  the  coupling  should  not  at  any  time  exceed  5°,  and  the  solution 
should  be  very  dilute  (about  i  %). 

The  excess  of  diazonium  salt  is  determined  by  spotting  on  filter- 
paper,  easily  soluble  dyes  being  first  salted  out.  As  a  suitable  reagent 
for  amines  or  easily-coupling  phenols  such  as  resorcinol,  a  solution 
of  R-salt  or  H-acid  is  used.  Some  factories  make  use  of  a  freshly 
prepared  solution  of  hydrocyanic  acid  which  gives  a  yellow  colora- 
tion. The  presence  of  excess  of  the  phenol  or  amine  which  is  being 
determined  is  ascertained  by  spotting  on  filter-paper  with  the 
diazonium  solution.  The  loss  so  caused  is  so  small  that  it  may  be 
neglected. 

(b)  Indirect  Determination. 

In  the  case  of  certain  amines  it  is  not  possible  to  estimate  them  by 
direct  diazotization  owing  either  to  their  forming  diazoamino  com- 
pounds or  diazonium  salts  which  blacken  starch-iodide  paper  in  the 


ANALYTICAL  SECTION  229 

same  way  as  free  nitrous  acid.  Amines  of  this  type,  e.g.  nitranilines, 
chloranilines,  etc.,  must  therefore  be  estimated  indirectly.  Thus, 
i/ioo  mol.  of  the  amine  in  question  is  dissolved  either  in  concentrated 
or  slightly  diluted  hydrochloric  acid,  poured  into  water  and  ice  and 
diazotized  with  a  fair  excess  of  sodium  nitrite.  The  clear  diazonium 
solution  is  poured  into  a  measuring  flask,  made  up  to  a  known  volume, 
and  is  then  run  in  from  a  burette  or  measuring  cylinder  to  a  strongly 
alkaline  |3-naphthol  solution  of  known  strength  until,  on  testing  on 
filter-paper,  no  naphthol  can  be  detected  with  diazonium  solution 
on  the  edge  of  the  spot.  Usually  the  quantities  are  so  chosen  that  the 
number  of  c.cs.  used  divided  into  100  gives  the  percentage  of  amine 
sought  for. 

Example:  3-45  gms.  ^-nitraniline  (=2'5/ioo  mol.)  are  dissolved 
in  10  c.cs.  hydrochloric  acid  of  30  %  strength,  and  10  c.cs.  water. 
The  clear  solution  is  poured  on  to  50  gms.  ice  and  50  c.cs.  water,  and 
is  then  treated  with  a  solution  of  2  gms.  100  %  sodium  nitrite  in  the 
form  of  a  20  %  solution.  Owing  to  the  slight  excess  of  nitrous  acid 
(about  0*2  gm.  NaNO2),  a  clear  solution  is  produced,  which  is  made 
up  to  250  c.cs.  in  a  graduated  flask.  100  C.cs.  of  this  solution  are 
measured  out  into  a  cylinder,  and  are  then  added  by  degrees  with 
stirring  to  a  solution  of  1*44  gms.  100  %  /3-naphthol  dissolved  in 
2  c.cs.  of  30  %  NaOH  to  which  20  gms.  sodium  carbonate  in  300  c.cs. 
ice  water  have  been  added.  By  means  of  spotting  tests  the  point  is 
determined  at  which  j8-naphthol  ceases  to  be  indicated  with  diazonium 
solution  on  the  rim  of  the  spot.  The  number  of  c.cs.  of  nitraniline 
solution  used  divided  into  100  (loo/c.cs.)  gives  the  percentage 
required.  If  the  nitraniline  is  100  %  pure,  then  exactly  100  c.cs. 
will  be  required.  Usually  101-102  c.cs.  are  needed. 


Estimation  of  Naphthols, 
f$-Naphthol. 

1*42  Gms.  (=1/100  mol.)  naphthol  are  dissolved  in  2  c.cs.  caustic 
soda-lye  of  30  %  strength,  and  25  c.cs.  of  10  %  sodium  carbonate 
solution  are  added.  Ice-cold  diazobenzene  solution  is  then  run  in 
from  a  measuring  cylinder  or  an  ice-jacketed  burette  until  a  drop 
tested  on  filter-paper  no  longer  forms  any  orange-red  dye  on  its 
edge  when  tested  with  diazonium  solution.  Owing  to  the  presence 
of  impurities  a  coloured  line  sometimes  forms  after  a  few  seconds 
where  the  paper  has  been  touched,  but  the  colour  is  always  muddy, 
and  with  a  little  practice  can  always  be  distinguished  from  the  pure 


23o  ANALYTICAL  SECTION 

naphthol  colour.  The  number  of  c.cs.  used  gives  directly  the 
percentage  composition  of  the  /3-naphthol.  A  good  quality  product 
should  be  at  least  99*5  %. 

a-Naphthol. 

a-Naphthol  couples  much  more  readily  than  ^8-naphthol,  and 
would  give  too  high  values  in  alkaline  solution.  For  this  reason  the 
coupling  is  effected  in  acetic  acid  solution  in  the  following  manner  : 
the  a-naphthol  is  dissolved  up  in  the  same  way  as  the  /3-naphthol, 
and  is  then  precipitated  with  dilute  acetic  acid  in  presence  of  25  c.cs. 
of  25  %  sodium  acetate  solution.  The  coupling  is  then  effected  as 
described  for  /3-naphthol,  and  as  soon  as  the  reaction  for  a-naphthol 
has  disappeared  the  whole  is  dissolved  up  by  adding  caustic  soda 
solution,  after  which  it  is  reprecipitated  with  acetic  acid  ;  "  aniline 
solution  "  is  added,  and  so  on  until  the  a-naphthol  reaction  has 
really  completely  gone.  Frequently  it  is  necessary  to  add  as  much 
as  30  %  of  the  diazo  solution  subsequently  owing  to  the  naphthol 
being  carried  down  with  the  precipitated  dye. 

Only  a-naphthol  can  be  estimated  in  this  manner,  as  /3- naphthol 
does  not  couple  in  acetic  acid  solution.  If  it  is  subsequently  desired 
to  estimate  the  /3-naphthol  content  as  well,  diazotized  nitr aniline 
solution  is  added  until  all  the  /3- naphthol  has  been  coupled  up.  In 
this  way  it  is  possible  to  estimate  both  naphthols  in  an  impure 
specimen  of  a-naphthol. 

Dihydroxynaphthalenes  (M.w.  160). 

These  are  determined  in  the  same  way  as  for  a-naphthol.  They 
couple  up  very  quickly  and  the  "  after-coupling  "  is  usually  very 
pronounced  and  impure,  so  that  it  is  easy  to  determine  the  end- 
point. 

Aminosulphonic  acids. 

i /i oo  Molecule  of  the  acid  is  dissolved  in  the  requisite  amount 
of  sodium  carbonate  solution,  which  is  then  diluted  to  250  c.cs., 
25  c.cs.  concentrated  hydrochloric  acid  are  added  and  the  whole 
titrated  with  normal  Nitrite  solution.  The  number  of  c.cs.  multiplied 
by  10  gives  the  percentage  composition.  Care  must  be  taken  only 
to  spot  the  nitrite  paper,  as  it  is  impossible  to  get  accurate  results  if 
the  paper  be  stroked  with  the  rod. 

Notice  should  be  taken  of  the  fact  that  very  energetic  diazonium 
salts  can  themselves  turn  the  starch-iodide  paper  blue  rapidly,  and 
it  is  also  essential  to  know  the  relative  sensitiveness  of  the  paper. 


ANALYTICAL  SECTION  231 

Sulphanilic  acid,  metanilic  acid,  and  naphthylamine  sulphonic  acids 
are  diazotized  at  15°. 

Cleve  acids  cannot  be  determined  so  easily,  as  they  couple  up  at 
once  with  themselves.  In  this  case  it  is  best  to  add  the  greater  part 
of  the  nitrite  to  the  neutral  solution  and  then  to  acidify,  stirring 
well.  Or  the  solution  may  be  diazotized  directly  at  o°,  nitrite 
being  added  until  the  violet  coloration  first  produced  changes  to  a 
pure  brown.  The  indirect  nethod  is,  however,  to  be  preferred,  as 
it  is  more  rapid. 


Estimation  of  Aminonaphthol  Sulphonic  Acids. 

Two  different  determinations  are  always  made.  First  of  all  the 
amount  of  nitrite  required  is  measured  and  this  figure  is  termed  the 
"  Nitrite  figure."  Then  the  amount  of  diazonium  solution  needed  is 
determined,  this  figure  being  known  as  the  "  Coupling  figure."  If 
both  figures  agree  we  know  that  the  melt  has  been  done  correctly, 
but  if  the  nitrite  figure  is  too  high,  we  may  conclude  that  the  melt 
has  been  too  short,  whilst  if  it  is  less  than  the  coupling  figure  the 
temperature  of  the  melt  was  too  high.  A  properly  prepared  amino- 
naphthol  sulphonic  acid  should  give  nitrite  and  coupling  figures 
which  agree  to  within  less  than  i  per  cent. 

It  is  hardly  necessary  to  add  that  all  these  estimations,  as  in 
all  cases  of  quantitative  analysis,  should  be  done  in  duplicate. 

Aminonaphthol  disulphonic  acid  1:8:3:6:  (H-acid}. 

(a)  Nitrite    figure     (calculated     upon     the    acid    sodium    salt, 
mol.  341) :   3*41  gms.  H-acid  are  dissolved  in  5  c.cs.  of  10  %  sodium 
carbonate  solution,  diluted  to  250  c.cs.,  precipitated  with  25  c.cs. 
concentrated    hydrochloric  acid  and  diazotized  at  5°  with  normal 
nitrite.     The  H-acid  should  give  a  fine  yellow  diazo  compound 
which  separates  in  beautiful  crystals  on  salting  out.     The  number 
of  c.cs.  used  multiplied  by  10  gives  the  percentage. 

(b)  Coupling  figure  :  3*41  gms.  H-acid  are  dissolved  in  50  c.cs.  of 
10  %  sodium  carbonate  solution,  which  are  then  diluted  to  300  c.cs.; 
and  N/io  diazobenzene  solution  is  then  added  until  a  slight  excess  is 
present.     To  test  this  a  little  heap  of  salt  is  placed  upon  a  piece  of 
filter-paper,  and  to  it  is  added  a  few  drops  of  the  red  solution.     After 
waiting  five  minutes  the  colourless  rim  is  touched  with  the  diazotized 
aniline  solution.     If  H-acid  is  still  present  a  red  rim  is  at  once 
produced.     If  diazo  solution  is  in  excess  a  drop  of  H-acid  solution 


232  ANALYTICAL  SECTION 

will  also  give  a  red  rim.  The  last  portions  of  H-acid  often  separate 
out  but  slowly  from  the  dye  so  that  towards  the  end  it  is  necessary 
to  wait  for  a  quarter  of  an  hour.  At  the  very  end  there  is  always  a 
more  or  less  strong  after- coupling.  The  purer  the  H-acid  the  fainter 
this  after-effect.  The  nitrite  figure  for  a  good  H-acid  is  about 
0*3  %  higher  than  the  coupling  figure.  The  number  of  c.cs.  of 
aniline  solution  used  gives  the  percentage  composition. 

All  the  aminonaphthol  disulphonic  acids  and  monosulphonic 
acids  are  determined  in  this  way.  The  diazonium  solution  is  placed 
in  a  100  c.c.  measuring  cylinder,  and  the  percentage  read  off  directly. 
Many  works  use  ice-jacketed  burettes  which  are  very  neat,  but  some- 
what complicated.  For  stirring,  a  stirring  rod  is  used,  the  end  of 
which  is  bent  round  in  a  big  loop.  The  coupling  is  carried  out  in  a 
clean  porcelain  dish. 


Estimation  of  Naphthol  Sulphonic  Acids,  Disulphonic 
Acids,  and  of  Dihydroxy  Naphthalene  Mono-  and  Di- 
Sulphonic  Acids. 

Example  :    Neville  and  Winther's  Acid  (—  Naphthol  sulphonic  acid 

1:4).    M.w.  224. 

The  acid  is  coupled  with  N/io  aniline  solution  exactly  as  described 
for  H-acid,  the  dye  being  salted  out  in  the  dish  towards  the  end  of 
the  reaction  so  that  it  becomes  easy  to  determine  the  remainder  of 
the  acid.  Using  2*24  gms.  of  the  acid  the  number  of  c.cs.  of  aniline 
solution  used  up  gives  directly  the  percentage  of  H-acid.  The 
coupling  is  effected  at  o°. 

SchafTer-salt,  R-salt,  and  other  naphthol  sulphonic  acids  are  also 
estimated  in  the  same  way.  Sultones,  however,  must  first  be 
hydrolysed  by  treatment  with  a  little  hot  caustic  soda. 

Dihydroxynaphthalene  mono-  and  di-sulphonic  acids  couple  up 
so  rapidly,  even  as  regards  the  second  coupling,  that  the  reaction  is 
effected  in  acetic  acid  solution  in  presence  of  sodium  acetate,  by 
means  of  aniline  or  the  more  energetic  ^-aminoacetanilide.  In  many 
cases  the  coupling  takes  several  hours,  e.g.  with  dihydroxynaphthalene 
disulphonic  acid  1:8:3:6  (chromotrope  acid),  and,  in  addition,  the 
resultant  colouring  matter  separates  out  from  the  unchanged  chromo- 
trope acid  only  slowly  owing  to  its  great  solubility,  so  that  great  care 
must  be  taken. 

It  is  sometimes  possible  to  estimate  various  sulphonic  acids  in 
presence  of  one  another,  but  the  results  obtained  are  rarely  accurate. 


ANALYTICAL  SECTION 


233 


For  instance,  Schaffer  salt  (sodium  naphthol  sulphonate  2:6)  can  be 
determined  fairly  accurately  in  presence  of  R-salt  (sodium  naphthol 
disulphonate  2:3:6)  in  the  following  manner  :  first  of  all  the  total 
amount  of  material  capable  of  being  coupled  up  is  estimated  with 
"  aniline  solution."  Another  portion  is  then  dissolved  in  as  small  a 
quantity  of  water  as  possible,  and  to  it  is  then  added  twenty  times  its 
volume  of  96  %  alcohol.  The  R-salt  is  precipitated  and  the  residue 
can  be  analysed  for  its  Schaffer  content  whilst  the  disulphonic  acid 
can  be  estimated  in  the  extract.  It  is  necessary  to  shake  up  the 
precipitate  with  the  alcohol  (after  mixing)  for  half  an  hour  as 
otherwise  too  much  SchafFer  salt  is  occluded. 

An  alternative  method  consists  in  first  estimating  the  total  by 
means  of  aniline  solution  and  then  removing  the  Schaffer  salt  from 
a  second  portion  by  means  of  formaldehyde.  For  example,  5  gms.  of 
the  mixture  are  dissolved  in  100  c.cs.  water,  5  c.cs.  pure  30  % 
hydrochloric  acid  are  added  and  2*5  c.cs.  40  %  formaldehyde,  and 
the  mixture  heated  on  the  water-bath  for  an  hour,  after  which  the 
disulphonic  acid  is  determined.  The  difference  between  the  two 
figures  gives  the  content  of  mono-sulphonic  acid. 

Yet  a  third  method  may  be  noted,  the  Iodine  method,  which 
depends  upon  the  following  fact.  Iodine  reacts  with  R-salt,  and  also 
with  Schaffer  salt,  preferably  in  the  presence  of  sodium  bicarbonate. 
The  mixture  is  first  titrated  directly  with  N/io  iodine  solution,  using 
an  excess  of  this,  and  then  titrating  back.  Another  sample  is  then 
separated  by  means  of  alcohol,  as  noted  above,  and  the  extract 
titrated  again.  This  method  is  believed  by  the  Elberfeld  works  to 
be  the  best,  as  the  coupling  method  gives  too  high  results,  and  so 
far  as  can  be  ascertained  this  contention  appears  to  be  correct, 


Test  Papers. 

(i)  Red  and  blue  Litmus  paper. — This  is  used  as  an  indicator  for 
all  weak  and  strong  bases  and  acids.  It  is  turned  red  by  acids  and 
blue  by  alkalis. 

Preparation  :  Best  quality  litmus  should  be  used.  The  cubes, 
containing  50-90  %  of  calcium  sulphate,  are  ground  up  and  extracted 
once  each  with  benzene  and  with  alcohol.  4  or  5  Gms.  of  the 
substance  are  then  dissolved  in  a  litre  of  water,  and  pure  filter-paper 
is  soaked  in  the  solution. 

To  dry  the  paper  it  is  hung  up  on  threads,  and  the  sheets  are 
then  cut  up  into  strips.  For  red  litmus  paper  a  few  drops  of  acetic 
acid  are  added  to  the  solution,  whilst  ammonia  is  used  for  the  blue 


234  ANALYTICAL   SECTION 

paper.  The  less  pronounced  the  coloration  of  the  paper  the  more 
sensitive  it  is. 

(2)  Congo  Paper. — Used  for  strong  acids.     It  is  rendered  a  pure 
blue  by  mineral  acids  and  violet  by  strong  organic  acids. 

Preparation  :  0*5  gms.  concentrated  Congo  Red  are  dissolved 
in  a  litre  of  water  and  5  drops  acetic  acid  are  added.  Filter-paper 
is  soaked  in  the  warm  solution  and  allowed  to  dry  in  a  clean  place. 

(3)  Thiazole  Paper  (Mimosa  Paper). — Used  for  free  alkali.     It 
is  coloured  a  pure  red  by  alkalis,  and  is  much  preferable  to  Turmeric. 
It  is  prepared  in  the  same  way  as  Congo  paper,  except  that  the  acetic 
acid  is  omitted.     Ammonia  is  without  influence  upon  this  paper 
even  in  high  concentrations. 

(4)  Phenolphthalein    Paper. — It    is    turned    red    by    alkalis.     It 
reacts  with  ammonia  and  with  sodium  carbonate,  but  not  with 
bicarbonates.      It  may  be  used  with  advantage  for  the  more  accurate 
types  of  analysis. 

Preparation  :  i  gm.  Phenolphthalein  is  dissolved  in  i  litre  of 
hot  water,  and  filter-paper  is  soaked  in  the  hot  solution. 

(5)  Starch  Iodide  Paper  (Nitrite  Paper). — Used  for  nitrous  acid 
and  for  hypochlorites.     It  becomes  bluish- violet  with  a  trace  of 
oxidizing  agent,  and  deep  brown  with  excess.     Care  must  be  taken 
that  the  paper  is  merely  touched  with  the  drop  of  solution  and  that 
the  glass  rod  is  not  scraped  across  it. 

Preparation  :  10  gms.  of  pure  starch  are  ground  up  with  a  little 
water  and  the  paste  is  then  poured  into  a  litre  of  boiling  water  with 
good  stirring.  After  cooling,  2  gms.  potassium  iodide  are  added,  and 
pure  filter-paper  is  soaked  in  it  and  allowed  to  dry  in  a  clean  atmo- 
sphere. This  paper  will  indicate  clearly  in  a  i  %  hydrochloric  acid 
the  addition  of  a  single  drop  of  normal  nitrite  per  litre  ;  it  is  thus 
extremely  sensitive. 

(6)  Lead  Paper. — Used  for  detecting  hydrogen  sulphide. 
Preparation  :   Filter-paper  is  soaked  in  a  solution  of  5  gms.  lead 

nitrate  per  litre,  and  is  then  dried  in  an  atmosphere  free  from  sul- 
phuretted hydrogen.  Instead  of  this  paper  one  may  use  paper  soaked 
in  a  solution  either  of  ferrous  sulphate  or  of  lead  acetate. 


Solutions  of  Reagents  used  for  "Spotting  M  on  Filter-Paper. 

(i)  H- acid  solution. — i  %,  with  5  %  sodium  carbonate.  This 
solution  is  used  to  indicate  the  presence  of  easily  coupling  diazo 
compounds  in  the  rim  of  spots  on  filter-paper.  In  place  of  H-acid, 
R-salt,  )8-naphthol,  hydrocyanic  acid,  etc.,  may  be  used. 


ANALYTICAL   SECTION 


235 


(2)  Resorcinol  solution. — i  %,  with  5  %  sodium  carbonate.    This 
is  used  for  detecting  any  diazo  compound,  even  those  which  do  not 
react  with  H-acid  (e.g.  Aminonaphthol  sulphonic  acid  1:2:4). 

(3)  Diazotized  p-Nitraniline. — This  reacts  with  phenols  and  with 
amines.     It  must  be  preserved  in  the  dark  and  will  give  a  yellow 
coloration  with  sodium  carbonate  alone  after  1-2  days,  so  that  care 
must  be  taken  in  its  use.     o-Chloraniline    may    be    used    equally 
well  in  place  of  />-Nitraniline. 

(4)  Alkali   sulphide   solution. — For    detecting    heavy    metals    in 
solution  such  as  Iron,  Copper,  Tin,  etc. 


Evaluation  of  Zinc  Dust. 

i  Gm.  of  zinc  dust  and  4*00  gms.  sodium  bichromate  are 
dissolved  up,  and  the  solution  made  up  to  a  litre  with  the  addition 
of  20  c.cs.  of  20  %  sulphuric  acid. 

250  C.cs.  of  this  solution  are  taken  and  diluted  up  with  900  c.cs. 
water.  150  C.cs.  of  20  %  sulphuric  acid  are  added  and  100  c.cs.  of 
10  %  potassium  iodide.  This  solution  is  allowed  to  stand  in  the  dark 
for  half  an  hour  and  the  excess  of  iodine  titrated  back  with  N/io 
thiosulphate. 

In  order  to  determine  the  strength  of  the  bichromate  exactly 
0*800  gm.  is  treated  in  a  similar  manner. 

Calculation  :  If  B  =  c.cs.  thiosulphate  for  0*800  gm.  bichromate, 
A  —  c.cs.  for  4  gms.  bichromate  plus  zinc  dust, 
then  %  metallic  zinc  =  (B  X  1*25— A)  X  1*308. 


Evaluation  of  Lead  Peroxide  Paste. 

About  3-5  gms.  of  a  good  average  sample  of  the  paste  is  weighed 
out  accurately  between  two  watch  glasses.  5  Gms.  of  Mohr's  salt 
is  then  added,  and  the  whole  rinsed  into  a  200  c.c.  flask.  The  mixture 
is  then  heated  up  on  a  boiling  water-bath  for  half  an  hour  and  25  c.cs. 
concentrated  sulphuric  acid  are  added. 

It  is  boiled  up  once,  and,  after  cooling,  the  excess  of  Mohr's 
salt  is  titrated  back  by  means  of  potassium  permanganate. 


INDEX 


"  A  "  PRICE,  219 

Acetanilide,  70 

Acetyl  H-acid,  114 

Acid  Anthracene  Red  G,  115 

Acid  Black  46,  130 

Acid  coupling,  125 

Acid  Orange  A,  113 

,  costing,  218 

Acid-resistant  iron,  203 

tanks,  207 

Alizarin,  167 

—  melt,  1 68 
Alkaline  couplings,  113 

Alkali  fusions  (summary  of  methods),  187 

Alkylations,  74 

Alkyl  chlorides,  method  of  introducing 

into  autoclaves,  75 
Alsace  Green  N,  51 
Aluminium,  use  of,  205 

—  thiosulphate,  176 
Amido-G-salt,  35 
Amidonaphthol  Red  6B,  115 

G,  31,  114 

Amines,  diazotization,  108 
— ,  estimation,  227 
/>-Aminoacetanilide,  69,  71 

as  an  azo-component,  142 

in  analysis,  232 

diazotization,  135 

Aminoazobenzene,  133 

—  condensed    with   nitrochlorbenzene, 
136 

Aminoazo-o-toluene,  178 
/>-Aminodimethylaniline,  175 
Aminodiphenylamine  sulphonic  acid,  50 
Aminochlorbenzoic  acid,  185 
Aminonaphthol  disulphonic  acid  1:8:2:4 

(Chicago  acid),  30 
—  disulphonic  acid  1:8:3:6  (H-acid),  10 

—  sulphonic  acid-i:2:4,  50 

--i:8:4'(S-acid),  30 

2:5:7  (J-acid),  35-41 

2:6:8  (Gamma  acid),  35,  40 

acids,  estimation,  231 

o-Aminophenols,  azo  dyes  from,  137 
Aminophenyl-tolylamine  sulphonic  acid, 
50 


Amino  sulphonic  acids,  estimation  of 

230 

Analytical  section,  224 
Aniline,  55 

—  Black,  56 
— ,  costing,  221 

— ,  diazotization,  108 

— ,  preparation  of  Normal  solution  of, 

226 

o-  and  £-Anisidine,  73 
Anthracene  Brown  FF,  170 
Anthragallol,  170 
Anthraquinone,  95 

disulphonic  acid,  167 

Auramine  G,  161 
—  OO,  159 

Autoclaves,  notes  on,  193 
— ,  erecting,  197 
— ,  laboratory,  198 
— ,  rotating,  200 
— ,  rules  for  using,  200 
Azidur,  205 
Azines,  178 
Azobenzene,  56 

—  disulphonic  acid,  62 

Azo  components,  coupling,  in 

—  Dark  Green,  123 

—  dyes,  1 08 

—  Flavine  FF,  136 
salicylic  acid,  185 

—  Yellow,  117,  129,  131 

-  G,  132 
Azoxybenzene,  56 

—  disulphonic  acid,  62 

Azoxy  compounds,  formed  in  reduction , 
17,  67 


"  BAKE  "  process,  43 
Bengal  Blue,  173,  218 
Bechamp-Brimmeyr  reduction  method) 

i? 
Benzaldehyde,  87 

—  disulphonic  acid  1:2:4,  149,  150 
Benzal  chloride,  87 
Benzhydrol,  147 

Benzidine,  56,  59 

—  tetrazotization,  no 


INDEX 


237 


Benzidine  colours,  118 

azo-salicylic  acid,  118 

2:2-disulphonic  acid,  62 

diazotization  of,  115 

Benzo  Fast  Blue  FF,  142 

FR,  141 

Scarlet,  211 

—  Purpurine,  128 
Benzoic  acid,  88 
Benzo  trichloride,  88 
Benzyl  chloride,  88 
Biebrich  Scarlet,  135 
Bindschedler's  Green,  175 

,  thiosulphonic  acid  of,  175 

B«-dehydrothio-/>-toluidine,  1 53 
Bismarck  Brown  G,  116 

R,  117 

"  Black  Convention,"  127 
Brilliant  Yellow,  139 
Bucherer's  process,  101 


CALIBRATED  vessel  for  coupling,  112 

Cast-iron,  uses,  203 

Caustic  soda  solution,  vapour  pressure 
curve,  202 

Celestine  Blue,  173 

Centrifugal  mills,  216 

Charges,  213 

Chicago  acid,  30 

Chinese  hair  cloths,  209 

Chloramine  Yellow  FF,  152,  155 

Chloranilines,  estimation  of,  229 

Chloraniline  sulphonic  acids,  diazotiza- 
tion, no 

2-Chlorbenzaldehyde,  93 

Chlorbenzene,  83,  86 

— ,  sulphonation  of,  43 

o-Chlorbenzoic  acid,  185 

Chlorine,  drying  of,  83 

Chlorinations,  83 

Chlornitro toluene,  90 

Chlorsulphonic  acid,  as  a  sulphonating 
agent,  45 

/>-Chlorsulphophenylhydrazine,  139 

2:6-Chlortoluidine,  90 

Chrome  Brown  R,  67 

Chrome  tanning,  97 

Chromium  sulphate,  97 

Chromic  acid,  regeneration  of,  181 

Chromocitronine,  115 

Chrysophenine  GOO,  139 

Ciba  Grey  G,  165 

—  Red  G,  165 

—  Violet  B,  165 

3B, 165 

Clayton  Yellow,  155 
Cleve's  acids,  23,  142,  182 

,  estimation,  231 

Clusiron,  205 

Columbia  Black  FF,  23,  26 

Compressed  air,  214 


Congo  paper,  234 

Congo  Red,  127 

Copper,  205 

— ,  as  catalyst  in  diazo  reactions,  52 

— ,  deleterious  action  of,  47,  98 

Costing  Department,  211 

—  of  a  dye,  example,  218 

Cotton,  209 

Cresidine,  142 

o-Cresol,  recovery  of,  106 

o-Cresotinic  acid,  106 

Coupling  figure,  231 

—  of  azo  components,  in 

— ,  summary  of  methods,  187 

Cyanosis,  55 


DEHYDROTHIO-/>-TOLUIDINE,  153 

,  sulphonation  of,  43 

Denitrating  towers,  87 
Dephlegmation,  85,  188 
Dextrine,  217 

Dialkylanilines,  technical  details,  104 
Diamine  Brown  V,  119 

—  Fast  Red  F,  119 

—  Green  B,  122 
G,  124 

—  Pure  Blue,  74 
Diamino-dibenzyl  disulphonic  acid,  95 

diphenylamine  sulphonic  acid,  49 

phenazthionium  chloride,  178 

stilbene  disulphonic  acid,  93-94 

,  diazotization  of,  no 

Diamond  Black  PV,  210 

Dianil  Brown  3GN,  61,  120 
Dianisidine,  74 
— ,  diazotization,  no 
Diazoamino  benzene,  133 

o-toluene,  178 

Diazosulphanilic  acid,  64,  130 

Diazotization  of  amines,  108 

— ,    determination   of   end   point   with 

dyes,  143 

2:6-Dichlorbenzaldehyde,  89,  92 
2:6-Dichlorbenzal  chloride,  92 
Dichlorbenzene,  84,  85 
2:6-Dichlortoluene,  91 
Diethylaniline,  102 

Dihydroxynaphthalene,  estimation,  230 
— ,  sulphonic  acids,  estimation  of,  232 
Dimethylamine,  52 
Dimethylaniline,  102 
Dinaphthylamine,  100 
Dinitraniline,  87 
w-Dinitrobenzene,  54 

—  sulphonic  acid,  46 
Dinitrochlorbenzene,  83,  86 

—  disulphonic  acid,  43 
Dinitrocresol,  77 
Dinitrodiphenylamine,  87 
Dinitronaphthol,  77 

disulphonic  acid,  77 

Dinitrophenol,  87,  158 


238 


INDEX 


Dinitro  stilbene   disulphonic   acid,    935 

94 

toluene,  69 

Diphenylamine,  97 

— ,  influence  of  copper  on  yield,  98 

— ,  distillation  of,  99,  190 

Diphenyline,  57 

Direct  Deep  Black  EW,  61,  125 

-  V,  127 
Disazo  dyes,  135 
Disintegrator,  217 
Distillation  in  vacuo,  188-193 
—  with  superheated  steam,  81,  99 


ENAMEL,  208 
Epsilon  acid,  184 
Erika  Red  type,  155 
~.Z,  iS5 
Erio  Chrome  Azurol,  92 

Black  A,  T,  52 

Blue  Black  B,  52 

Flavine  A,  185 

-  Red  B,  137 
—  Glaucine,  93,  148 
Ethylbenzyl  aniline,  102 
Evaporators,  multiple  effect,  214 
"  Evaporating  down  to  salt,"  39 

FAST  light  yellow  G,  137 

-RedAV,  130 

-Yellow,  134 
Filter-cloths,  209 
"  First  price,"  219 
Formyl-/>-phenylene    diamine    colours, 

123 

Fractionating  column,  188 
Frederking  apparatus,  169,  190 
Fusion  pot,  7,  8 


G-ACID,  32,  34 
G-salt,  estimation  of,  228 
Gall-nuts,  107 
Gallamide,  106 
Gallamine  Blue,  171 
Gallic  acid,  106 
Gallocyanines,  173 
Gamma  acid,  35-40 

(wo-),  36,  4 1 

Gas  heating,  advantages  of,  190 
Glass,  uses  of,  208 
Grinding  of  colours,  216 


H-ACID,  10,  14,  19,  22 
— ,  estimation  of,  231 

— ,  melt,  19-22 

— ,  solubility,  20 
Heitzmann  superheater,  98 
Helianthine,  131 
Hemp,  uses  of,  209 
Hexanitrodiphenylamine,  87 


"  Homogeneous  lead  lining,"  206 
Hydrazobenzene,  57,  58 
—  disulphonic  acid,  62 
Hydrocyancarbodiphenylimide,  162 
Hydroxyanthraquinone  sulphonic  acid, 

167 
o-Hydroxyazo  dyes,  lake  formation,  137 

I.G."    See  "  Interessengemeinschaft." 
Indamine,  178 
Indanthrene,  210 
Indian  Yellow,  131 
Indigo,  161,  165,  210 
Indoines,  182 
Iiidulines,  134 
Intermediate  products,  3 
"  Interessengemeinschaft,"  211 
Iron,  uses  of,  203 
— ,  etching  of,  17 
Ironac,  205 
Isatin,  165 

a-Isatin  anilide,  162,  164 
Iso-y-agid,  36,  41 


J-ACID,  35-41 
Jute,  209 


KUBIERSCHKY  column,  85,  1 88 


LAUTH'S  Violet,  178  . 
Lead,  205 
-  paper,  234 

—  peroxide  paste,  evaluation  of,  235 
Leather,  uses  of,  209 
Leuco-Malachite  Green,  145 

Xylene  Blue,  149 

Linings  for  autoclaves,  195,  197 
Litmus  paper,  234 


MALACHITE  Green,  145 

Management  of  a  dye  factory,  213 

Manganese  mud,  150,  179 

Martius  Yellow,  77 

"  Mass  products,"  210 

Meldola's  Blue,  173 

Metachrome  Brown,  79 

Metals  used  in  the  dye  industry,  203 

Metanil  Yellow,  130 

Metanilic  acid,  41 

,  diazotization,  no 

Methylene  Blue,  174 
,  zinc-free,  177 

—  Green,  177 

—  Grey,  172 
Mikado  dyes,  94 
Mimosa,  156 

—  paper,  234 

Miscellaneous  azo  dyes,  129 
—  dyes,  161 


INDEX 


239 


Mixing  machines,  218 
Modern  Violet,  172-173 


NAPHTHALENE,  5,  79,  218 
/3-Naphthalene   sulphonic   acid,   4,    12, 

216 

Naphthamine  Yellow  NN,  152,  155,  211 
Naphthaquinone  monoxime,  51 
Naphtha sul tarns,  31 
Naphthasultone,  30 
Naphthazarine,  43 
Naphthionic  acid,  45 

,  diazotization,  no 

Naphthogene  Blue  4R,  141 
a-Naphthol,  1.02 
^-Naphthol,  4,  8 
— ,  costing  of,  219 
— ,  distillation,  190 
— ,  sulphonation,  32 
Naphthols,  estimation  of,  229 
Naphthol  Blue,  173,  218 
—  Blue  Black  B,  122 

—  disulphonic  acids,  estimation  of,  232 
acids  1:3:6  and  1:3:8,  155 

-  2:3:6  and  2:6:8  (R  and  G),  32 
Naphthol  sulphonic  acids,   estimation, 
232 

acid  1:4    (Nevile    and    Wintrier), 

101 

2:1,  32 

2:6  (Schaffer),  32 

Naphthol  Yellow  S,  77 
a-Naphthylamine,  79 
— ,  diazotization  of,  109 
/3-Naphthylamine,  98 
Naphthylamine  Black  D,  130 
a-Naphthylamine       disulphonic       acid 
1:2:4,  82 

—  sulphonic  acids  1:6  and  1:7,  23 
— ' 1:5  and  1:8,  27 

trisulphonic  acid  1:8:3:6,  10,  13 

/3-Naphthylamine       disulphonic       acid 
2:4:8,  184 

—  acids  2:1:5,  2:5:7,  2:6:8,  35 
Nerols,  50 
Nevile  and  Winther's  acid,  101 

,  estimation,  232 

Nickel,  use  of,  205 
ra-Nitraniline,  66 

—  diazotization,  108 

o-  and  ^-Nitraniline  diazotization,  109 
— ,  estimation,  229 
p-Nitraniline,  69,  72 

—  sulphonic  acid,  48 

—  dyes,  reduction,  123 
Nitraniline  sulphonic  acid  3:1:4,  46 

acids,  diazotization,  no 

Nitrations,  53 

— ,  summary  of  methods,  186 
Nitric  acid,  recovery  of,  87 
Nitrite  figure,  231 

—  paper,  234 
/>-Nitroacetanilide,  69,  70 


Nitroamino  phenol,  66,  87 

Nitrobenzene,  53 

— ,  costing,  221 

—  sulphonic  acid,  41 

Nitrochlorbenzenes,  utilization  of,  183 

/>-Nitrochlorbenzene, p-nitraniline  from, 
72 

o-  and  ^-Nitrochlorbenzenes,  sulphona- 
tion of,  43,  48 

jp-Nitrochlorbenzene  sulphonic  acid,  48 

Nitrochlorbenzoic  acid,  185 

,  reduction  of,  69 

Nitro  filters,  77,  170,  209 

a-Nitronaphthalene,  79 

—  trisulphonic  acid,  13 
,  reduction,  16 

o-  and  />-Nitrophenols,  73 

,  ethers  of,  73 

,  alkylation  of,  74 

Nitrophenol  sulphonic  acids,  reduction, 

69 

Nitrosalicylic  acid,  reduction,  69 
^-Nitroso  diethylaniline,  172 

—  dimethylaniline,  171 
Nitroso-jS-naphthol,  50 
Nitrosulphonic  acids,  instability  to  heat, 

16 

o-Nitro  toluene,  183 
/>-Nitrotoluene,  43 
Non-metals,  uses  of,  206 
"  Niitsch/'  9,  114 
N-W  acid.    See  Nevile   and  Winther's 

acid. 

"  OIL  of  Mirbane,"  89 
Oleum,  60  %,  advantages  of,  13 
"  On-costs,"  213 
Orange  II,  113 
,  costing  of,  218 

—  IV,  129 

Organic  structural  materials,  208 
Organization  of  a  dye  factory,  211 
Oxalyl-/>-phenylene     diamine     colours 

~I23 

Oxazines,  107,  171 

Oxidations,  93 

— ,  summary  of  methods,  186 

PARA  Red,  72 
Patent  Blue,  93 
—  class,  148 
—  Department,  212 
Peri  acid,  30 

Perplex  disintegrator,  217 
Phenetidines,  73 
Phenol  disulphonic  acid,  76 
Phenolphthalein  paper,  234 
Phenol,  coupling  of,  140 
— ,  nitration  of,  73 
Phenylamino-tolyl-indamine,  179 
Phenyl-azo-dinitro-diphenylamine,  136 
w-Phenylene  diamine,  67 

sulphonic  acid  1:2:4,  46 

Phenyl-gamma  acid,  101 


240 


INDEX 


Phenylhydrazine  sulphonic  acid,  64,137 
Phenyl  hydroxylamine,  56 

sulphonic  acid,  62 

Phenylmethyl  pyrazolone,  137 
Phenylnaphthylamine     sulphonic     acid 

1:8,30 

Phenyl-peri  acid,  30 
Picramic  acid,  77 
Picramic  acid,  dyes  from,  218 
Picric  acid,  76,  87 
Polar  Yellow  56,  138 
Ponceau  R,  33 
Porcelain,  use  of,  208 
Primuline,  152 
— ,  alkylation  of,  155 

—  sulphonic  acid,  diazotization  of,  no 
Primuline  Red,  154 

Propaganda  dye  house,  212 
Pyrazolone  dyes,  notes  on,  139 
Pyridine,  purification  of  anthraquinone 
by,  96 

R-ACID,  32-34 

Raschig  column,  85,  189 

—  rings,  77,  85,  189 

Reduction       by       Bechamp-Brimmeyr 

method,  17 
Reductions,  53 
— ,  technical  apparatus,  21 
— ,  summary  of  methods,  186 
Rfius  coriara,  107 
Rubber,  uses  of,  209 

S-ACID,  30,  184 
Safranine,  178 
Salicylic  acid,  105 
Schaffer  acid,  32,  33 

,  estimation  of,  233 

"  Schwarz  Konvention,"  127 
Silver  salt,  167 
Small-scale  plant,  212 
Sodium  nitrite,  estimation,  225 

,  standard  solution,  226 

Specialities,  210 
SS-acid,  30 
Standardization,  216 
Standards,  215 
Standard  dye-house,  215 

—  products,  21  o 
Starch  iodide  paper,  234 
Steam  consumption,  214 

—  distillation,  82,  99 

Stirring  with  reflux  condenser,  47,  84 
Stoneware,  uses  of,  206 
Structural  materials,  203 
Sulphanilic  acid,  43 

,  diazotization,  no 

,  costing,  221 

,  purification,  225 

Sulphochrysoidine,  120 
Sulphon  Acid  Blue  R,  31 
Sulphonating  pot,  5 
Sulphonations,  4,  45 
— ,  summary  of  methods,  186 


Sulphophenyl-methyl-pyrazolone,  137 
Sulphur  Black  T,  157 
Sulphur  melts,  152 
Sultones,  estimation,  232 
Swiss  Cavalry  Yellow,  139 

TANKS,  acid-proof,  207 

Tantiron,  205 

Technical  details,  188 

Test-papers,  233 

Tetramethyl-  diamino  -  dipheny  Imethane , 

159. 

Thiazine  Blue,  178 
Thiazole  paper,  234 
Thiazole  Yellow,  152,  155 
Thioamide,  161,  164 
Thiocarbanilide,  161,  163 
Thioindigo  Scarlet  R,  165 
ct-Thioisatin,  163,  165 
Thionine  Blue,  178 
Thio-oxamine   diphenyl  amidine,    162, 

164 

Thio-/>-toluidine,  153 
Tin,  uses  of,  205 
o-Tolidine,  diazotization,  no 

azo-o-cresotinic  acid.  118 

Toluene  disulphonic    acid    1:2:4,    149, 

152 
^-Toluene  sulphochloride,  uses  of,  104, 

139, 152 

Toluidine,  diazotization,  108 
— ,  utilization  of,  183 
Toluylene  diamine  1:2:4,  69 
o-Tolyl-indamine,  179 
Trihydroxyanthraquinone  1:3:6,  170 
Trinitrophenol,  76 
Triphenylmethane  dyes,  145 
Tropasoline,  129 

—  for  acid-black  mixings,  130 

—  nitration,  131 
Type,  215 

UVIOL  lamp,  93 

VACUUM  distillation,  188-193 

—  dryers,  216 

—  in  works,  214 

—  pumps,  189 
Vesuvine  R,  117 

WOOD,  uses  of,  208 

— ,   injurious   influence   of,    in   certain 

cases,  115,  124 
Wool,  uses  of,  209 
Works  chemist,  duties  of,  215 

—  management,  notes  on,  210 

XYLENE  Blue  VS,  93,  148 

—  Yellow,  138 

Xylidine,  diazotization  of,  108 

ZAMBESI  Black  V,  23 ,  26 

Zinc,  uses  of,   205 

Zinc  dust,  evaluation  of,  235 


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